Frontline War-Rager

The reward keys off a board state most aggressive red decks fall into by accident rather than by design: when your end step rolls around, count your tapped creatures, and if the number is high enough, the Kavu grows. No attack of its own is required, no combat math to sequence. The subtlety is that the trigger counts tapped bodies rather than attackers, so a mana dork that tapped for a spell, a creature that spent itself on an activated ability, and a body tapped to pay some other cost all feed the counter right alongside your swingers. What never counts is the creature you held back on defense: blockers stay untapped, so a board playing keep-away leaves the trigger empty even while it does exactly what you want. A go-wide offense makes the counter close to automatic; a stalled one leaves the Kavu sitting at its printed 2/3, waiting for the rest of the team to do the tapping. It never accelerates itself, always exactly one counter per end step, which is the restraint that keeps it from snowballing on its own. That habit of paying off aggression after the fact is an old red idea: a mid-cost body that gives a wide board a reason to keep it around and let it fatten, rather than trading it away early while it is still small.