Probably best use case is to reanimate this to cheaply unlock a Room
But if you manage to collect all five pieces in your hand, you win the duel - just like that
Flaming Fist gives your commander creatures double strike so that they can get the job done as quickly as possible
That doesn't sound like much, but it could be the difference between whether you're able to cast the spell you brought back that turn or not
Whenever you cast an instant or sorcery spell, this enchantment deals 2 damage to each opponent
Countering a spell for 2 mana has always been a good rate, and then giving you the ability to stop a power play while effectively stealing the benefits of an opposing Dark Ritual, Black Lotus, and/or Moxen on your next turn was powerful Magic then, and it is certainly not worse now