Colossus of Sardia Although someone ranked the 90s Shandalar PC game as one of the worst Magic video games (cough, cough), if you played it you likely have fond memories of trying to win with the biggest creature in the game, Colossus of Sardia, before you got your Black Lotus and Time Walks
if that hadnt come out, Id be telling you to sell those immediately
Shalai and Hallar turns +1/+1 counters into damage, and this deck is full of ways to put them on creatures and overwhelm your opponents
This will let you kill very quickly needing to deal 10 instead of 40 regular damage and 21 Commander to kill, and it will stay around for future kills, unlike Triumph
Additionally, it needs to attack to flip back, so it wont be blocking next turn, either
A sunrise for Plains, a rainstorm for Island, and a lush rooftop garden for Forest