Gargos, Vicious Watcher

The cost reduction is the reason to run it; the fight trigger is the reason it warps a game. Most Hydra payoffs care about the +1/+1 counters piled onto a single body; this one instead turns targeting into a hazard. The trigger fires whenever a creature you control becomes the target of a spell, and that scope is deliberately symmetric: an opponent's removal, bounce, or aura sets it off, but so does your own cheap pump or protection spell. That symmetry is the whole build-around. You can hand Gargos its fight yourself, using a one-mana trick on your own creature to force an 8/7 swing into their board at instant speed, then let the actual pump land afterward. Because it fights rather than deals one-sided damage, Gargos absorbs return damage too, so the trigger favors an 8/7 body swinging into things it comfortably outsizes; against smaller creatures it is a clean answer, against a fellow fatty a genuine trade. Vigilance means it holds that threat back while still attacking. The Hydra discount floods the board with the very targets that make the trigger dangerous, cheating out creatures like Voracious Hydra or Hydroid Krasis a full spell ahead of schedule. Both abilities push toward the same conclusion: any spell that touches your creatures, yours or theirs, should cost a creature on the other side of the table.