Well, let's have a looksey...
Smeargle Lv. 21
40 Hp
Basic
Colorless
Weakness: fighting
Resistance Psychic
Retreat cost: 1
C Paint
0
Flip a coin. If heads, choose a type (other
than Colorless) and put a Coloring Counter on the defending Pokémon.
That Pokémon is now the type you chose. If it already had a Coloring
Counter, remove the old one. If tails, this attack does nothing.
Okay, it is a pumped up Base Set Porygon, but
think about it.
Your opponent has a Sneasel with 4 Darkness
energies on it. Smeargle Paints them Psychic. During there turn,
they flip 5 coins and 3 heads. Due to Resistance, it only does
30 damage then Sneasel does 40 damage to itself. Considering you cannot
remove a counter without evolving, all of Smeargle's opponents (Blastoise,
Hitmonchan, Wigglytuff, Sneasel, Rocket's Zapdos, Electabuzz) will stay the
type you choose until they are returned to your opponent's hand. Just Retreat
Smeargle and Attack!