PVC-free polypropylene sleeves, no acid
In any 20 life game, like normal casual or multiplayer, the 3 life tax means it creates a strong tension between people who don't want to die and people who don't want you to have a recursive loop
The card is a part of an infinite combo in Modern that involves cards like Grist, the Hunger Tide and undying creatures
(Choose any number of permanents and/or players, then give each another counter of each kind already there.) If Kilo is tapped to station a permanent, its last ability will resolve before the station ability resolves
Really the only reason I consider Canyon Wildcat higher on the list is that its in red, which most Mountainwalk cards are
I don't expect to see these in 60-card constructed decks, but in Commander I can definitely see them having a profound impact