Synchronize

Effect:

Whenever this Pokémon is burned, paralyzed, poisoned or badly poisoned, the Pokémon who gave this Pokémon that ailment is also given the ailment. This ability passes back bad poison when this Pokémon is badly poisoned. This ability cannot pass on a status ailment that the Pokémon did not directly receive from another Pokémon, such as the poison from toxic spikes or the burn from a flame orb.

Synchronize is introduced in Gen 3: