This is a pseudocode overview of how Pokémon Showdown works - particularly relevant to anyone writing event code.

(A) = negated by Mold Breaker (and Turboblaze/Teravolt) on abilities only during a move
(S) = negated by Sheer Force only during a move with a secondary effect
(U) = negated by Substitute

(Air Lock and Klutz negates every event for the corresponding effect, so don't need to be marked)

=== MOVES ===

A quick overview of how moves work:

STEP 1. MOVE PRE-USAGE
	external execution interruption (flinch, full paralysis)
	"POKEMON used MOVE!"
STEP 2: MOVE USAGE
	internal execution interruption (charge turn for SolarBeam etc)
	move start of sub-move (Metronome, Sleep Talk etc)
	PP deduction
	STEP 3. MOVE EXECUTION (sub-moves start from here)
		there is no target
		internal move failure ("But it failed!")
		STEP 4. MOVE HIT (happens once per target)
			move misses
			external move failure (Protect, Substitute blocked etc)
			immunity
			move animation
			damage
			other effects
			secondary effects

=== MAIN LOOP ===

[BeforeTurn]
for every move:
	[ModifyPriority]
	move's [BeforeTurn]

runAction() - runs runSwitch, runAfterSwitch, and runMove in priority order, then residual at end {
	runSwitch() {
		[BeforeSwitch]
		switch
	}
	runAfterSwitch() - after all pokemon are switched in {
		[Switch]
		ability's [Start]
		item's [Start]
	}
	runMove() {
		[BeforeMove] (A)
		-> false => exit runMove

		display "POKEMON used MOVE!"

		useMove() {
			[ModifyMove] (A)

			if no targets:
				display "But there was no target..." and exit useMove()

			moveHit() - once for each hit of multi-hit move, and also once for secondary hits {
				move's [TryHit], [TryHitSide] or [TryHitField] (A)
				if hit:
					[TryHit] (A)
					-> 0 => skip to SelfHit (used for Substitute)
					-> null => exit moveHit()
					-> false => display "But it failed!" and exit moveHit()
				[Immunity] (A)
				-> null => exit moveHit()
				-> false => display "It had no effect!" and exit moveHit()

				move animation

				getDamage() {
					move's [BasePower]
					[BasePower] (A)
					move's [Damage]
					if critical hit:
						[CriticalHit] (A)
				}
				damage() {
					[Damage] (A,U)
					-> false => exit damage()
					damage
				}
				heal() {
					[Heal] (A)
					-> false => exit heal()
					heal
				}
				status() (U) {
					[Status] (A)
					-> false => exit status()
					status change
					status's [Start] (A)
					-> false => restore previous status and exit status()
					[AfterStatus]
				}
				effect() (U) {
					if effect already exists:
						effect's [Restart] (A)
					otherwise:
						effect change
						effect's [Start] (A)
						-> false => remove effect and exit effect()
				}

				recoil() {
					call damage()
				}
				drain() {
					call heal()
				}

				if hit:
					[SelfHit] (A)
				if secondary hit:
					[SecondarySelfHit] (A)

				if hit:
					if secondary roll succeeds:
						secondary() (S,U) {
							call moveHit()
						}
			}

			[AfterMoveSecondary] (S,U)
			[AfterMoveSecondarySelf] (S)

			[AfterMove]
		}
		pp deducted
	}
	runFaint() {
		[Faint]
	}
	residual() {
		for every effect:
			if duration = 0:
				effect's [End]
				remove effect
			otherwise:
				effect's [Residual]
	}

	choose switch-ins for fainted pokemon
	=> runSwitch() and runAfterSwitch() again

	[Update]
}



=== ISOLATED ===

These are not part of the main loop, and are only called from inside an event.

(For instance, eatItem() is usually called from within the Update event of a berry, and weather() is called
from the Residual event of a weather condition)

eatItem() {
	[UseItem] (A)
	-> false => exit EatItem()
	[EatItem] (A)
	-> false => exit EatItem()
	item's [Eat]
	remove item from pokemon
}

useItem() {
	[UseItem] (A)
	-> false => exit UseItem()
	remove item from pokemon
}

takeItem() {
	[TakeItem] (A)
	-> false => exit TakeItem()
	remove item from pokemon
}

setItem() {
	set item
	item's [Start]
}

setAbility() {
	set ability
	ability's [Start]
}

weather() {
	[Weather]
}