mtg mill card Rock 'n' (and a list of all MTG's mill cards) (Modern Deck) Weftwalking Enchantment counters discard and

The mutate trigger doesn't do much to excite me, though you could use it to clear away a blocker

That said, Proliferate is a lot more powerful when its magnifying your +1/+1 and loyalty counters, rather than compounding your opponents -1/-1 counters

Its controller may search their library for a basic land card, put it onto the battlefield tapped, then shuffle

As legendary creatures can distinctly be used to spearhead Commander decks, they are quite popular

#3 Aura Shards Every deck needs to run some number of enchantment or artifact removal, and Selesnya happens to have one of the best cards to do that in the game