Kalain, Reclusive Painter This is a tough category to narrow to one, but Kalain is the pick here because of the new archetype she helped fuel: red-black treasure
Even 1 damage dealt to a creature from a source with deathtouch is considered lethal damage, so any amount greater than that will cause excess damage to be dealt, even if the total amount of damage isn't greater than the creature's toughness
Its easy for a niche card to be strong within its niche - and sometimes a card like that is simply so strong that it takes a deck from being a fun idea into a crushing way to play Commander - but its far rarer for a card to work in decks that its not intended for
Dead Weight is looking better and better, and helps race us towards delirium
Great dual lands that will see play for years
Since both Feather and Dark-Dwellers have replacement effects on where that spell goes when it resolves, you get to choose which order these effects are applied