Defensive effects are a must in the game, but an incredibly pushed card like Mithril Coat might actually cause problems, and its downsides are negated in the Commander format
Thirty years ago, the answer to that question would have been a shoebox, but not anymore
Grinding Station Did you know theres only two cards in Magic with Grinding in the name, and theyre both mill spells
At large events like PAX, you can find deals on boxes that vendors cant move locally
There are also commanders that exploit life loss, with Ob Nixilis, Captive Kingpin, Valgavoth, Harrower of Souls, and Rakdos, Lord of Riots (its a very Rakdos-coded mechanic)
Forever, or at least until someone removes the enchantment since its a huge threat