I also recently had a cool game in Legacy where my opponent had a Sanctum of Prelate on one and a Thalia, Guardian of Thraben in play, while I had a Dress Down and Swords to Plowshares in hand with five lands in play including a fetchland
Mono-color samurai like Iizuka the Ruthless, Nagao, Bound by Honor, Opal-Eye, Konda's Yojimbo, and Sensei Golden-Tail just dont do enough or interact with a particularly relevant creature type
By effectively doubling the black mana output of your swamps, Cabal Coffers allows you to surge ahead of opponents, bringing a significant level of power to decks that invest heavily in this color
Fangs is one of the best green cards in MTG to solve that problem
Damage dealt to a planeswalker is not marked, but rather results in that many loyalty counters being removed from the planeswalkers (it's not marked damage according to the MTG rules)