You see, nobody wants to kill Regice, because they just did your job FOR you- getting it out of active
Courser gets you roughly a life and half a card each turn it is in play
Today, though, it's still having a major impact as one of the strongest card-draw finishers in cEDH and low-to-the-ground decks overflowing with fast mana, where Ad Nauseam can often draw you a massive chunk of your deck, giving you the fuel you need to win the game
These are decks like Rowlet & Alolan Exeggutor- GX /Vileplume, or a dedicated Garbotoxin deck
Learn more: Out of the Abyss Nihiloor ( Adventures in the Forgotten Realms Commander) A mind flayer named Nihiloor serves as a master spy for Xanathar, the beholder crime lord of Waterdeep
Then, on top of that, add light support, in the sense that it takes few card slots, that works for any tribes