How about double strike and extra combat
It provides a little ramp in the form of Treasure tokens, and allows you to sacrifice those Treasures to exile the top card from your library and play it that turn
However, if you do, and that permanent is an illegal target at the time the ability tries to resolve, the ability won't resolve and none of its effects will happen
(If a permanent with a stun counter would become untapped, remove one from it instead.) It gulps from the lava flow to spew gouts of molten rock upon its prey
And then, if you just attach one additional energy card, Darkrai can send anything to the discard pile with Abyss Eye as long as the Pokmon is affected by a special condition
Conversely, with Chronomaton the problem was that youd invest a lot of time and mana into a creature, and then when you finally got around to trying to do something with it your opponent could just kill it and youd have nothing to show for it but Hangarback Walker is very much the opposite unless your opponent has just the right removal spell