According to my in-game tests:
Poison Touch gives its bearer a 30% chance to cause poison with its
direct attacks (not 20% as was previously believed). This chance is
independent of the additional effect chance the attack may have.
For example, Poison Jab combined with Poison Touch
will result in a 51% chance to cause poison, and Crunch combined with Poison
Touch will result in a 6% chance to both decrease the opponent's Defense
and couse poison.
Accordingly, my description for Poison Touch now reads:
Whenever a non-bearer is hit by a direct attack by the bearer, that non-bearer may be poisoned (30% chance; considered an additional effect by Shield Dust but not Serene Grace; prevented by Safeguard and Substitute).
The items King's Rock and Razor Fang and the Ability Stench each gives all damaging attacks by their bearer a 10% chance to flinch the opponent, except if the attack already has an additional effect of causing flinching. Stench is not cumulative with King's Rock and Razor Fang, and vice versa. Accordingly, my description for these items and this Ability are now:
Stench:
Whenever a non-bearer is hit by a damaging attack by the bearer that doesn't have an additional effect of causing its opponent to flinch, that non-bearer may flinch this round (10% chance; considered an additional effect; not cumulative with King's Rock or Razor Fang; prevented by Substitute).
King's Rock/Razor Fang:
Whenever a non-holder is hit by a damaging attack by the holder that doesn't have an additional effect of causing its opponent to flinch, that non-holder may flinch this round (10% chance; considered an additional effect; not cumulative with Stench; prevented by Substitute).
lmitchell0012:
In addition to the things you mentioned, the opponent's base experience, the language version of the attacking Pokemon, and whether the player's Exp. Point Power is active (which is a power received by completing Entralink missions) can all influence how many Exp. Points a Pokemon can gain.