Diep.io reddit post.

NOTE: Before anyone gets angry, some of these ideas might resemble your ideas or someone else's. Since I don't exactly have the time to honeycomb the reddit, I'm apologizing beforehand. I'll try my best to edit my post to give links/credit as time goes on, but I probably won't be very active. Furthermore, the ideas in this will be extremely numerous, I'll be happy if one of these are implemented.
Also, I apologize for grammatical errors.( HAHAHAHA! GET ME NOW, GRAMMAR NAZIS!)

Shapes/Obstacles/Boosters:

So we have the square, triangle and pentagon, so I'm just going to continue from the 3 to 5 thing. Plus, it'll educate people about the names of shapes :D. The first three of these will have defense mechanisms, possibly more than three.
Septagon:
 Since there’s the primary colors, let's start with the complementary. I would say one side is orange, the other green, or one green, the other purple, etc. If that looks bad, vertically or just one color. The score will be 600, 5x that of a pentagon, and about three times the health. It's "ability" will be that whenever someone shoots at it or is close to body ramming it, a concentrated burst (maybe 3 bullet's on each side, with the same damage as a few points in bullet damage ((2-3)) with 2-3 points in bullet speed. They'll last for a little while, but not enough to take out an Assasin/Sniper. The cooldown for this is five seconds.

The idea here is that that the bullet's will make the septagon survive enough to survive a few casual hits from a big guy, or 1 hit from a Destroyer. If the Pentagon spawns every ten squares, the septagon spawns every 30 to 40.

Nonagon:
Purple core surrounded by a layer of orange, then green.
The Nonagon has three times the score of the Septagon, or as much as an alpha pentagon, and 0.8 times the health of an Alpha Pentagon. The Nonagon has a shield of rapidly rotating bullets. 1/5th of the shield is replenished every 5 seconds, and it takes a few seconds from a triplet/gunner to destroy the shield. How the Nonagon replenishes the shield: There's a tiny cannon on each side of the Nonagon, which has the damage of a Bullet Damage maxed out Sniper bullet (If that's too weak, maybe an Assasin). The Nonagon can also shoot high-speed bullets out of the shield.

This is hard to defeat. The shield is far enough away from the Nonagon that a tank can fit inside the space between the shield and the shape. See what I'm getting at here? If you're something like a Triplet/Gunner (bullet damage tank), quickly sneak into the part of the shield you destroyed, and begin going to town on the shape. Be careful, cause the cannon on each side deals damage-you may have to make an opening to break out if you're at low health. If you're a body damage build, like a destroyer, use bullets to destroy the shield, but ram it instead. These'll provide a nice alternative besides the Alpha Pentagon's at middle. They will be 7 to 15 in the map at one time.

Dodecahedron: Now it's getting real. 1.5x the health of an Alpha Pentagon, and a whopping 15k score. Has a glowing yellow-ish aura around it which will come into use later. (The aura is 1-2 squares wide.) I'm thinking lots of gold and silver lines intersecting each other, with a black background. That, or the old fashioned rainbow. Has a gun on every other side of it, that fires at the frequency of a twin, and the damage of a maxed out bullet damage machine gun.  Bullet's don't travel a far distance, though. Any shape that the bullets hit becomes controlled like a Necromancer (Yes, even Pentagons, Septagons, not Nonagons though, they just die from the bullets)  and follow and attempt to eliminate any player nearby. If nobody's around, they passively circle around the Dodecahedron, so Stalkers actually have to aim. (:P) Finally, about the Aura. Every few seconds it crackles with lightning and gives a high damage AOE effect. Good luck.

Triplet/Gunner/Fast Shooting Tank Strategy:
Try to avoid the hexagon of bullets as much as you can. The bullets don't have high penetration, so you can slowly pick off the shape army as they chase after you. After that, the Dodecahedron is weak-hit it with all you got. Careful for Pentagon's forming behind you and hitting you. (A note: all shapes controlled by the Dodecahedron do 1.5x more damage than usual. It's imperative to shoot down the Septagons before they ram into you.) When your health gets low, retreat and come back for another go.

Body Damage Build Strategy: It's unlikely you'll be able to tank the shape army, so try and pick of a few with bullets (A very accurate Destroyer shot may be able to destroy ~5 at once!) and destroy the rest. Dodge as many bullet's as you can and start ramming. Beware the Aura, you'll notice that it's about to hit when the aura glows brighter than usual. Since it might be a little unfair, let's say Body Damage is slightly buffed against a Dodecahedron. Finally, in FFA, you could have one each at the NW corner of the map and the SE corner to take attention away from the middle, having them regenerate every 3-5 minutes. In Team DM/Domination, maybe they can be surrounded by Alpha Pentagons. (Can't be controlled) And provide a share of EXP to everyone who killed it, person who got the last shot in gets a 15% bonus.

Pluses: (Note: someone mentioned something similar to this, I replaced the permanent points with a temporary big buff) These would be extremely rare (3-5 times rarer than a Nonagon?) drifting plus signs that have the health of two pentagons, and have a different color depending on their stat. Say, if there's a Movement speed Plus, and if I destroy it, my Movement speed gets buffed to 150% for 1/2 minutes. That plus would be light blue, since Movement Speed is light blue. So if you find one, go for the leader.

Level Orb:  2 per map. Don't need to say much more. Has health of an Alpha Pentagon and everyone is shown where it is via an arrow. Gives SEVEN levels no matter what level you are. A cool color scheme would possibly be a black and white yin yang.

Turrets: (Again, someone mentioned this, I gave it more complexity) Destroy it to claim it, has 1/2 health of an Alpha Pentagon. Only in FFA and Team DM. (Teammates can't destroy/ be hurt by it.) If you claim it, you have the option to go into "Turret Mode" anytime you want to (In Turret Mode your EXP goes to the turret.) You can Level it up to any Level 15 Tank, but the Bullet Damage is multiplied by 1.5. It has three upgrades, which is equivalent to leveling it up to 45. (I know, it's a lot, but just wait.) Invisible: Invisible unless an enemy is close. Moving: You get the idea. Control it like Overseer triangles. Homing Shots: Even more obvious.

Castles/Fortresses: (Again, someone did this,  I won't have boss monsters, just a turret.)A Castle has walls made of squares, which are invincible. Inside is a turret, though it is leveled up to 30. (No Invisible, Moving, Homing.)

Fortresses have walls made of invincible triangles, and five rooms (1 surrounded by 4) each room has a turret, which has to be cleared before proceeding to the next room. Middle room is last. Middle room has a level 45 turret with homing shots. (For your info, Overseer/Necromancer/Overlord triangles are more accurate and move faster.) All turrets are random selected, for Castles and Fortresses.

Upon defeating a Castle/Fortress, all squares/triangles die and are converted into points, You get an additional 2k score if it's a Castle, and 8-10k if a Fortress. Turrets disappear. Castles/Fortresses would be ok in all modes, with 7 Castles per map and 3 Fortresses.

I promise, no more structures, no need to make the map more cluttered.

Mode Ideas: Everyone has said Team DM Deluxe or something (4 teams) so I'll pass on that.

bucklakeluki (His post is pretty much at the top in this thread) had a Castle Siege idea, I'm thinking something like a Turret that each team has to capture, that gains moving when you capture it.
Basically, CTF, as many people said. A Time Limit idea where you have ten mins to level up and face a Boss (Level 60 tank) and hide and seek was very interesting. A few players with Arena Closer builds, everyone has to hide/kill those two players, possibly have the map flooded with castles/squares to make hiding easier, and the hiders have maxed movement speed, or where those players are Stalkers would be cool. Basically, I have no ideas, so I'm improving everybody's ideas and posting them here. Yes, I'm a no-life.

New Tank Ideas:
Wrecking Tank:
Has a large, dark grey ball attached by a chain. Builds up momentum as you swing it, bullet damage affects damage, reload affects recovery speed if ball is damaged, bullet pen. is essentially the health of the ball, and bullet speed is speed. Either has no gun, or a few weak ones.

Double Wrecker (Level 30 branch off of Wrecking Tank): Has two balls, but reduced damage. Slightly increased movement speed.

Launcher (Other Level 30 branch off.): You can launch the Wrecking ball via spacebar at a Destroyer maxed out bullet speed velocity. If it hits nothing (not counting any shape besides Nonagon or the Dodecahedron) It slowly comes back. If it hits something, it disappears and takes 5-10 seconds to recharge. Has four weak guns in the North direction, South, East, West.

Demolition Expert (Level 45 branch off of Double Wrecker): Can control balls. Gains guns like the launcher. There is no chain, and one wrecking ball is slow but powerful and is controlled by right click, and the other fast but weak and controlled with left. Try to herd people into the damaging one.

Mace (Level 45 branch off of Launcher): Has spikes on the ball which can be launched by pressing space bar again. Timing is EVERYTHING. Has four guns that have stronger bullet speed, damage, and reload. The Wrecking ball has ten spikes, which each do 1/10 damage of wrecking ball. Damage of wrecking balls to be decided, idk.
Note: All Wrecking ball classes have increased heath.

Cluster Shot (Lot of people have got something like this, I tried to make mine unique). Shoots bullets that have 4/7 damage of sniper, at the same rate of a Sniper, that after hitting something or 2 seconds explode into small bullets.

Incendiary Gunner (Level 30 branch off of Cluster Shot): Obviously, bullets are burning. Does 1.5x bullet damage over two seconds, and has a second cannon. Fires slightly slower.

Gas Gatling (Level 30 second branch off of Cluster Shot): Shoots much faster, bullets explode into a cloud of gas which poisons and slows players. Body Damage increased......

Fireworks (Level 45 branch off of Incendiary Gunner): Each cluster bullet splits into EVEN MORE bullets, everything incendiary. The tank now (with a slow rate of fire, duh) fires a large firework shaped bullet.

Choke 'Em and Poke Em' (Level 45 branch off of Gas Gatling.):
First of all, I know, horrible name. Gas slows down more, body damage/health increased.

Note:  Classes below only for Team DM/Domination.

Barricader: Builds a wall of squares via spacebar (call me Trump) that's 1-2 inches wide, the squares have 4x the health of average squares. Perfect for giving teammates that are under fire a chance to run/recover. Cooldown of 15 seconds, also fires a machine gun that has decreased damage.

Iron Wall (Level 30 branch off of Barricader):
Wall made of 4x health triangles instead. Machine gun has slightly increased bullet pen, speed, reload, damage. (As good as a normal bullet damage maxed out machine gun.)
Upgradable Wall (Other level 30 branch off of Barricader):
Can shoot bullets at the wall. Every bullet shot makes the wall a tiny bit stronger. Wall extremely vunerable when you’re upgrading it.
The Pentagon (Level 45 upgrade off of Iron Wall):
Wall surrounds you like a Pentagon. Teammates and you can pass in and out.  A note: Overseers and Overlords can steal Triangles from your walls-slowly.
Reflective Design (Level 45 upgrade off of Upgradable Wall): Bullet’s shot at the wall are reflected back at ¾ the damage and 1.5x the speed. It’s hilarious watching Gunners accidentally kill themselves.
Medic (A Ton of People have suggested this. I have a very interesting design.):
Two paths, one must take one at level 30. One of good and one of evil. For right now, though, ramming into people increases their health. Except enemies, of course. Health healed depends on health regen and max health upgrades. Is equipped with a 7/10 sniper damage cannon, which fires at the same speed as a sniper. Healing gives exp too.
Battlefield Medic (Level 30 branch off of Medic):
Health increased. Cannon recoil increased. Ramming into people now depends on how much momentum you can build up.
Injector (Other level 30 branch off of Medic):
You are now equipped with a slow firing (Destroyer rate) syringe gun. Bullet speed increased. If someone on the enemy team is hit, their health slowly decreases for 15 seconds and their movement speed is halved. Health decreased.
War Paramedic (Level 45 branch off of Battlefield Medic):
You are now equipped with a triple shot gun. Can be changed from healing mode to damaging mode. Damage and health regen increased.
Pandemic Shooter (Level 45 branch off of Injector):
Shoots slower. Virus now cripples bullet penetration and does more health damage, but cannot kill. Only lasts for 8 seconds however.
Level 60 Upgrades: (I’m giving only a summary of each upgrade cause I’m super tired.)
Grimlord (Someone suggested this, I’m forwarding it-Level 60 branch off of Necromancer.):
Has fifty spaces. Triangles take 5, pentagons 10, squares 1.5. Can press space to explode a random shape in possession.
Persuant (Level 60 branch off of Stalker):
Invisibility is retained while moving, not shooting. Bullet speed increased.
Octoshield  (Level 60 branch off of Octotank):
Gains a shield similar to Nonagon. Spacebar to shoot out parts of shield. Has machine gun on four sides.
Chainsaw (Level 60 branch off of Booster): Front gun turns into high damage chainsaw, which can also cut bullets in half, making them useless. Cannons on back gain more thrust.
Multitude (Level 60 branch off of Fighter):
Cannons on back gain different abilities. One shoots homing triangles, the other poison bullets, another flamethrower, last one slowing bullets. Front gun shoots destroyer bullets.
Focused QuadraShot (Level 60 branch off of Triplet):
Self explanatory.
Septashot (Level 60 branch off of Pentashot):
More guns = GOOOOD!!
Laser Scope (Level 60 branch off of Ranger):
Gains zoom in feature, FOV increased, bullet damage increased.
Equipment Overload (Level 60 branch off of Demolition Expert):
Gains two medium speed, medium damage wrecking balls. Guiding controls are switched to arrow keys/WASD.
Cannonball (Level 60 branch off of Mace): Ball now explodes after a random time. Spikes have increased damage. (Explosion deals AOE damage.)
Gas Mines (Level 60 branch off of Choke Em’ and Poke Em’):
Can place up to seven mines, press spacebar to explode all, 1-7 to explode a particular one. Gas has improved paralysis. FOV increased.
4th of July (Level 60 branch off of Fireworks):
Gains second gun on back. Incendiary damage increased, reload time decreased.
Trapper (Level 60 branch off of The Pentagon):
Pentagon now looks like a spider’s web, and is made of regular septagons. Health increased. Movement speed increased. Run up to an enemy to trap them. Health degrades, but cannon go to zero in “web” (Only for enemies) Web is triple layered, and auto-frees lower tier players who don’t have the firepower to get out. Takes 1/3 of their health though. Takes approximately 20 seconds to get out with Octotank.
Portal Walls (Level 60 branch off of Reflective design):
Can place up to three walls. When a bullet hits a wall (doesn’t matter if ally or enemy) it is teleported to another wall and bullets values are increased by 1 in 2 fields that are randomly picked. Does not function if only 1 wall is placed. Wall can still be destroyed.
Spirit Link (Level 60 branch off of War Paramedic):
Healing bullets have increased healing. Health increased. Has an ability which can be used every 1 and a half minutes: Sacrifices ¾ of tank health and transfers to a target player which has to be selected. Range of a quarter of the map.
Mad Doctor/Hypnotist (Don’t know which name is cooler-Level 60 branch off of Pandemic Shooter):
Shoots very slowly, bullet speed slightly increased, penetration significantly increased. Has a cooldown of 1 minute-shoot an enemy player to immobilize them for 10 seconds (got to have some creepy stuff) and turn them to your side for 1 ½ minutes. The higher someone’s score is, the more shots it takes.
WOOOO IM DONE OMG. THIS WAS 2868 WORDS LOL.