After a review of the disassembled code of gens 1 and 2, we've come to realise some very important stuff regarding secondary status.
On gens 1 and 2, Fire-types are not inherently immune to burn.
Ice-types are neither inherently immune to ice.
On gen 1, secondary status effects for paralyse, burn, and freeze will be ignored if the target Pokémon shares a type with the move-type.
On gen 2, the same happens but only for burn and freeze.
Poison-types are actually immune to poisons.
On gen 2, tri-attack can burn fire-types and freeze ice-types.
On gen 1, body slam cannot paralyse normal-types.
Also, Lick cannot paralyse ghost-types.
And thunderbolt/thunder can't paralyse electric-types.
Normal damage is calculated with boosts, screens, and burn.
If a critical hit happens, then:
Stat level modifications are ignored if they are neutral to or favour the defender.
Reflect and Light Screen defensive boosts are only ignored if stat level modifications were also ignored as a result thereof.
If the attacker is burned, stat level modifications are always ignored.
The attack drop from the burn is only applied when attacker's attack level is higher than defender's defense level (boost).
Therefor:
A critical hit will ignore defensive and offensive buffs/debuffs if the attacker and the defender have the same boost level or the defender has higher boost.
The boosts will be ignored if the attacker is burned, but if the attacker has more boost than the defender, burn reduction still applies.
Burn reduction won't apply on the first case, buffs being the same or defender having more.
This fixes issues with a lot of moves, including but not limited to Acid, Beat Up, Bone Rush, Crunch, Dig, Extreme Speed, Fake Out, Future Sight, High Jump Kick, Hypnosis and Petal Dance.
In Gen 2,moves with negative priority work with negative speed.
It's the slower phazing move that will work first.
To achieve this, gen 2 runs its own compare priority and the functions
which use this one are edited so they use the custom compare priority.
