As long as you haven't yet chosen to do that this turn, all instances of sacrificing a creature will cause Riveteers Ascendancy's ability to trigger
With such weird cards being printed, Wizards of the Coast has had to find ways to make sure people don't accidentally put a card with Denimwalk (can't be blocked by a player wearing denim) or Art Menace (can only be blocked by creatures with two or more characters in their art) into their normal Magic decks
Haste + Vigilance Because youre so often attacking with your haste creatures, you dont have a chance to block with them
With eight Stuffy Dolls, we almost always find one early in the game, which is really important since it's super unlikely that our deck will win without a Stuffy Doll
Into the Flood Maw If you are playing Blue, you start your list with four copies of this card
While those are both great choices, my favorite that we are going to build around today is Karrthus, Tyrant of Jund