Abrupt Decay is fantastic against low-curve control decks, or even tempo decks looking to stick a cheap threat and back it up with cheap countermagic
It provides immense flexibility because it hits multiple useful card types, and even if you mull down to 1 you're still seeing more cards than an opponent who has taken 0 mulligans
(If a creature with a shield counter would be dealt damage or destroyed, remove a shield counter from it instead.) Shield counters don't prevent players from sacrificing creatures
However, in any deck that plays a lot of legendary creatures, it's one of the best cards you can be playing
Ill also exclude digital-only cards from MTG Arena like You Line Up the Shot, which lets you conjure a Plummet into your hand, acting as a dedicated hate card against fliers
The Treasure token you get on turn 2 by beholding a dragon kicks things off quickly