Amumu tips

Strengths:
1. Safe, fairly quick clear.
2. Some of the best CC in the game
3. Extremely strong ganking tool
4. %HP damage as well as spammable damage ability.
5. Tanky, good peeling
6. Ability to kill squishies with only 1 or 2 damage items.
7.
Weaknesses:
1. Weak to counter jungle early game
2. Telegraphed abilities, fairly easy to dodge engage
3. Fairly weak engage if you miss your Q
4. Forced to use flash to land good ults against coordinated teams
5. Ult doesn't stop ability usuage, meaning its not as strong against casters.
6. Weak against duelests.

Tips:
1. Start E or W in the jungle (E vs raptors/wolves, W vs buffs)
2. Max E, put 2-3 points in Q, then max W.
3. Amumu can solo objectives like dragon and rift herald fairly safely once he gets a few levels in his W. Use this to get your team ahead if you can't gank.
4. Amumu is weak to counter jungle early game, but has a strong level 3 gank if you land your Q. Use this to get a lane ahead early or force the enemy to use
summoner spells.
5. Save Q until your sure you can land it, going for max rank Qs is risky and likely will miss, minimizing your ganking effectiveness. Holding onto your Q will also psych
out the enemy to try and side step, making it easier for your laner to catch up and deal damage.
6. Don't use your ult too sparingly waiting for the perfect 5 man ult, landing the CC on priorty targets (ADC, Mid, etc) can singlehandedly win teamfights.
7. Amumu is incredibly strong if used properly, but lacks the "solo carry" ability of better scaling champions like Jax, Yi and Udyr. He is an "enabler"
this means that you can turn team fights by CCing important targets, peeling for your carrys, and zoning off enemies. You'll likely die in most teamfights unless its
incredibly one sided but thats ok. Dying in order to secure objectives or multiple priorty kills for your team is very much worth it.
8. Amumu's newly buffed passive makes him a strong pick in AP heavy comps allowing for your team to do large amounts of bonus true damage.

Builds:
Because this is a low elo guide, team comps will usually fall into a few basic compisitions:

VS heavy AP:
Cinderhulk, Abyssal mask, Liandries, Adaptive helm/Spirit visage, Gargoyle stoneplate, Merc treads.

VS heavy AD:
Cinderhulk, Thornmail, Randuins/Frozen Heart, Zhonyas, Gargoyle, Merc treads/Tabis depending on the CC

VS balanced team:
Cinderhulk, Abyssal mask, Thornmail, Liandries, Gargoyle's Stoneplate, Merc treads/Tabis depending on the CC

On team with low damage:
Runic Echos, Zhonyas, Liandries, Rylais, Banshee's Veil, Sorc boots.

Runes: Resolve: Aftershock, Font of life, Conditioning, Overgrowth. Precision: Triumph/Presense of mind, Legend: Tenacity. Stat bonuses: AP,AP, Armor or AS, Armor, Armor.

Finishing thoughts: Amumu is a very strong champion in low elo because teams tend to teamfight very often, and your ult and AOE damage allows for your team to have a
huge advantage in those fights. The only reason he gets weaker the higher elo you go is your enemies will get a better sense of how to avoid those ultimates and force
amumu to go into less than ideal situations. They also will learn to punish amumu's weak early game and starve him out or invade and kill him with stronger junglers.
Despite all this, there is a reason why amumu was part of the legendary "Bronzodia" comp back in the day. Learn to play him, he's not that hard and he will reward you
pretty quickly.