Procedurally-generated metroidvania design doc (the "Game")

Gameplay focus is on the following aspects:
1) Exploring procedurally-generated environments
2) Finding powerups to unlock new areas of the map
3) Fighting monsters with a combination of melee and ranged weaponry
4) Ultimately defeating [a|some] boss[es]

Survival should be difficult; the player has limited health resources and
health pickups are uncommon -- mostly only dropped by bosses or found as
one-time pickups.

In the interests of making gameplay more chaotic (and thus harder to survive)
without being unfair, a simple physics system comparable to Spelunky's will be
implemented. This will support:
 * Basic ballistic trajectories for uncontrolled (stunned) entities
 * Gravitational attractors/deflectors
 * Inelastic tethers

Most roguelike games need a source of variety to maintain interest in different
games. Some examples:
 * Dungeons of Dredmor's build-your-own-class skill system
 * Binding of Isaac's gigantic list of possible powerups
 * Spelunky's chaotic physics and unforgiving damage system
 * Rogue Legacy's varied classes and grinding system
 * Angband's 500+-long list of monsters

Common sources of variety to many roguelikes:
 * Themed regions
 * Procedurally-generated items (enchanted gear, etc.)
 * Large numbers of enemy types (even if only superficially differentiated)

The Game will have the following sources of variety:
 1) Varied powerup list, of which only a subset will be seen in any given game
    (See Item List, below). Adding variety this way is difficult (each item
    must be coded and the map generator must take items into account).
 2) Varied monster list, with a large set of differing behaviors. See Monster
    List, below. Adding variety this way is somewhat difficult (each monster
    must be individually coded but is self-contained).
 3) Scaling map generation by difficulty (so the same "room" will be different
    depending on when in the game it shows up, to make it easier/harder to
    navigate). For example, platforms may be smaller, spikes can be added,
    more or harder monsters can be placed. Adding variety this way is
    relatively easy.
 4) Varied map regions (see Region List, below). Adding variety this way is
    straightforward but time-intensive: new graphics and rooms must be added.
 5) Configurable game modes (see Challenge List, below). Adding variety this
    was is very easy (for most modes), but the scope for each challenge is
    limited and most will probably be played at most one time per player.
 6) Setting up the possibility for sequence breaking (bypassing locks) through
    skilled play (see Advanced Techniques, below). Adding variety this way is
    difficult (the map generator must be intelligent enough to preclude the
    possibility of the player getting stuck) but is thematically important.


Item List:
At base, the player can run, jump, and make grounded and aerial melee attacks.
 * Bladed melee weapons, which deal more damage and give a spinning aerial
   attack to cover a better area of effect (also enable enemy bouncing; see
   Advanced Techniques). Can cut through some materials (e.g. vines).
   * Could be upgraded to deal more damage and cut through harder materials.
 * Electrically-charged blades ("taser blades"), which temporarily stun
   enemies. Stunned enemies can be used as platforms.
   * Could be upgraded to short out shielding used by enemies or as locks.
 * Unsharpened high-inertia blades (a.k.a. lead bars), less damage but knocks
   enemies around.
   * A.k.a. suit strength upgrade? Include an aerial slam attack?
 * Jump boots, enabling higher basic jumps.
 * Jump jets, enabling double jump.
 * Buddy pods. A variety of different pods can be found, only one of which can
   be active at a time. The pod follows the player around, hovering above
   their shoulder. Their activatable abilities consume ammo, which is
   replenished via pickups dropped by monsters. Should ammo be shared between
   pods?
  * Shield pod. Blocks ranged attacks that hit it and can be activated for a
    brief full-body shield effect. Possibly larger than other pods.
   * Possible upgrade: can be emplaced as a temporary platform / barricade?
  * Missile pod. Fires an explosive missile.
  * Teleport pod. When activated, pod holds current position; activate again
    to teleport to it.
  * Cloak pod. Makes the player invisible for a short period, which prevents
    enemies from reacting to them and makes them invisible to laser tripwires.
  * Point Defense pod. Toggle active/inactive; automatically attacks nearby
    enemies while active at the cost of some ammo (fires a laser?).
  * Scout pod. When activated, can fly around and scout the area / fit into
    small regions. Possibly an upgrade for the teleport pod (fly pod behind
    enemy then teleport to bypass/access weak point) or the missile
    pod (fly-by-wire missile launcher)? Alternately can attack with an area
    electric shock (c.f. taser blades) and disrupt circuits
  * Leash pod. When activated, flies forward and attaches to a monster; that
    monster is then leashed to the player. It cannot move on its own, but
    swings under the influence of the tether and gravity; colliding it with
    other monsters stuns them. Is this usable in a lock/key system?
 * Magnetically-charged boots which allow walking on metal walls/ceilings.
   Turns such surfaces into gravitational attractors.
 * Magnetically-coupled grappling hook, allows swinging from metal
   walls/ceilings. Uses a tether system.
 * Speed booster. Tap boost when running (with a cooldown between taps) to
   increase speed, up to four times. At max speed, player is invulnerable,
   breaks certain blocks, and can perform a powerful dash attack.
 * Jetpack, allowing limited flight (duration resets every time player lands)
 * Electroproofing, allows safe passage on/through charged surfaces (an
   environmental hazard)
 * Supercavitation bubble (or something more scientifically plausible), allows
   free movement through water.
 * Hazardous environment protection (heat, poison gas, radiation, etc.). Such
   environments deal damage and affect controls in various unpleasant ways.
 * Vertical grappling hook. Shoot it up, then retract to climb. Possibly an
   early version of the more generically-useful grappling hook? How to make
   this interesting?


Monster List:
Monsters should have simple behaviors, for ease of implementation, but ideally
should require different tactics on the part of the player to be dealt with.
 * Wall-walkers (basic monsters that patrol the perimeter of the terrain)
  * Worms (I saw an image of a section of orange that would make a good worm-
    type image, with the skin of the section removed so it was just the little
    juice capsules)
  * Spiders
  * Rotating disc robots
  * Two pods connected by an (intangible) chain; one acts as a pivot and the
    other rotates about it, then they switch roles (c.f. digger bot in
    Super Metroid)
 * Fliers:
  * Hang on ceiling and swoop at the player when they pass below
   * Bats
  * Fly continuously in various patterns
   * Horizontal back-and-forth patrol (c.f. Metroid invincible monsters)
   * Bouncing sinusoidal patterns
 * Spawned monsters (small, weak monsters that are produced by monster
   spawners)
  * Fly up/down to level of play, then fly horizontally
  * Make repeated hops towards player (at higher difficulties, hops are
    irregularly-paced and irregularly-sized)
 * "Hazard" monsters:
  * Venus Flytraps that capture the player (or other monsters) when they step
    on a trigger (which may be more or less subtle depending on difficulty)
  * Pits full of fleas, that jump on the player and explode shortly
    thereafter, bouncing the player around
  * Monster spawners that continuously create other monsters (and may or may
    not be invulnerable themselves)
 * Land monsters, that may walk a small patrol, and perform one of a few
   behaviors when the player gets close:
   * Fire a projectile
    * Humanoid guards
    * Gun turrets
    * Homing missile turrets
   * Perform a melee attack
    * Scorpions
   * Jump into the air, perform an action (fire projectile, etc.), land.
    * "Hedgehogs" (painful to attack in melee, the idea being the player would
      rather avoid them)
    * Tigers (lunge at the player when they get close)


Region List:
Caves: rocky terrain, mossy walls, mushrooms
Deep caves: like caves, but more red; fungus gets livelier and "glowier"
(c.f. Phazon Mines in Metroid Prime), magma


Challenge List:
The goal here is to provide a variety of "play modes" that would give the
player things to do beyond just playing the game over and over. Most of these
would modify the "base rules" in some way, which would be:
 * Unlimited lives (but kicking the player back to savepoints on death)
 * "Standard" density/count of powerups
 * "Standard" difficulty span across the game
Challenges:
 * Limited lives (up to only one life) with savestations acting to "suspend"
   the game instead of making a checkpoint
 * Preselected item lists specifically chosen to be hard and/or strange (e.g.
   starting the player with a jetpack but no offensive abilities, in a high-
   difficulty region)
 * Beat the game without collecting all the key powerups (making sequence
   breaking mandatory, in other words)
 * Heaven Or Hell: everything (including you) dies in one hit.
 * Speedrun mode: an advancing wall of death continuously forces you to
   progress (using a special linearized map generator)


Advanced Techniques:
 * Secret shortcuts. Some terrain (indicated by subtle tile variations) is
   destructible and allows locks to be bypassed.
 * Walljumps. These should be roughly as difficult to perform as in Metroid
   Zero Mission.
 * Booster jump. After performing a max-boost attack, the player will briefly
   be in a special "landing pose". Jumping from this pose sends the player
   flying in a straight-line trajectory (c.f. Metroid shinespark).
 * Booster Short Charge. The boost level does not reset to 0 unless the player
   stops moving forward; thus by only holding forward when boost is pressed,
   the max-level charge can be achieved in a shorter distance.
 * Monster bouncing. Perform a melee attack (c.f. bladed melee upgrade, above)
   against certain invulnerable flying monsters and get bounced off of them.
   With proper timing this can be used to "jump" off of monsters without
   stunning them with the taser blades.