When you play Light Machamp from your hand, if it is on your Bench, remove 3 damage counters from your Active Pokémon. If it has fewer damage counters than that, remove all of them. Then, switch Light Machamp with your Active Pokémon.
If the Defending Pokémon has Dark in its name or is a Darkness Pokémon, flip a coin. If heads, this attack does 100 damage instead of 50.