A card must already be exerted in order to be challenged, meaning you cant challenge characters played on your opponents last turn
Doling out these counters each turn is a boon in any game format or deck type, and Jenova already has some great combos with other +1/+1 counter-focused creatures like Ouroboroid
Given that this card is yet again popping up on a bonus sheet, this time as a source material card, it's expected to continue being live only in formats such as Commander, Historic, and Modern as opposed to Standard or Brawl
If enough creatures die during a single turn, it transforms into Sephiroth, One-Winged Angel, the final major boss of FF7
The Emerald cards give you plenty of indirect ways to mess up your opponent's plans, meaning that this is a slow-burn deck where every play counts if you want to win
Probably the most expensive Legendary in the set for a while