Other known variants
x2Darkest Impulse
As long as Dark Ampharos is in play, whenever your opponent plays an Evolution card from his or her hand to evolve 1 of his or her Pokémon, put 2 damage counters on that Pokémon. You can't use more than 1 Darkest Impulse Poké-Body each turn.
RamShock BoltDiscard all Lightning Energy attached to Dark Ampharos.
This Pokémon is both Lightning Darkness type.
Can I use Team Rocket's Ampharos' "Darkest Impulse" Ability to put 4 damage counters on both of my opponent's evolving Pokemon if they evolve two Pokemon from their hand during the same turn?
Yes, you can. The phrase "doesn't stack" means that if you had two Team Rocket's Ampharos in play, you would not be able to use both Darkest Impulse Abilities to put 8 damage counters on each of those evolving Pokemon.
If I have Team Rocket's Ampharos with the "Darkest Impulse" Ability in play and my opponent's Team Rocket's Zubat with 40 damage evolves into Team Rocket's Golbat, do I get to use Team Rocket's Golbat's "Sneaky Bite" Ability before it gets KO'd?
Yes, you can. Since both Abilities are happening at the same time, the owner of Team Rocket's Golbat gets to choose the order they are applied.