Like so many other recurring mechanics without an official name, this has been named after the first card where it appeared, Act on Impulse
While only affecting a single creature type restricts Cavern, typal decks can leverage this to ensure their threats get through countermagic, be they efficient merfolk, monstrous dinosaurs, or sneaky goblins
Additionally , Mega Rayquaza ex serves as the flagship card of the expansion
They were 0/1 colorless creature tokens with the ability "Sacrifice this creature: Add ." Rise of the Eldrazi was all about getting giant Eldrazi creatures onto the battlefield, so the set needed help with mana
While those plays can be proactive, you arent short on reactive responses with morphers, either