Hystrodon

The morph cost and the draw trigger are pointed at the same problem, which is what makes this beast more than a slow green dork. A 2/2 with no abilities sitting across the table forces a guess: trade with it, let it through, or block to deny whatever it might become. Pay mid-combat and the answer is a 3/4 with trample that wants contact regardless of how the block resolves, because trample shoves damage through chumps and the connection cashes in for a card. An opponent who blocks the small body to stop the beats walks into a flip and a draw; one who blocks the flipped creature with a small body still bleeds trample damage. The keyword is doing the load-bearing work on the trigger: a vanilla attacker gets chump-blocked into nothing, but trample lets excess damage land to fire the draw on many connections. The payoff sits in green's least comfortable axis. Repeatable card advantage off creatures is usually blue or black territory; here it comes attached to a body that grows past what it shows and replaces itself with a card every time it lands combat damage on a player. That grind-while-you-beat-down loop, wrapped in the bluff of a face-down body, is morph at its most disciplined: the reward is real but it costs mana to deploy, mana to flip, and a successful connection (not just a swing) to collect.