Environmental Scientist makes me very happy
If you pay no mana, youre trading two resources for one of your opponent's
The actual way that the card will typically function is that each player will choose a number (and write it down to prevent them from changing it later and to prove they were thinking of that number), and each player will lose life equal to that number with the player who wrote the smallest number losing half of their life
Its a powerful effect, gated slightly by the three to play, three to equip
Notably, since Commander is typically played in four-person pods, Tifa can trigger her own ability so long as you attack each of your opponents with at least one creature during the same combat phase
After a while, it became a staple of the tournament scene because it allows control decks to reliably kill without playing any creatures at all, turning lots of their opponents' cards useless by denying them targets