MANAHIVE

Equivalent cards (G, “Creature — Human Warrior”, cares about counters, can grow itself):

• “Pelt Collector” (gets +1/+1 counters as other creatures with greater power enter or die)
• “Experiment One” (Evolve: grows with bigger creatures, can remove counters for regeneration)
• “Gyre Sage” (Evolve: gets +1/+1 counters, taps for G per counter)
• “Avatar of the Resolute” (enters with counters for each other creature with a +1/+1 counter, has trample)

These all share some synergy with counters and creature growth, similar to “Hydra Trainer.” None have exert, but the adapt and counter mechanics are matched.