Ariados

Spider Web

Flip a coin. If heads, the Defending Pokémon can't retreat. (Benching or evolving that Pokémon ends this effect.)

Poison Bite

20

If this attack damages the Defending Pokémon, the Defending Pokémon is now Poisoned and you remove a number of damage counters from Ariados equal to half that damage (rounded up to the nearest 10). If Ariados has fewer damage counters than that, remove all of them.