Vinebred Brawler

The trigger fires the instant you declare the attack, in the Declare Attackers step, before any blocker is assigned: another Elf you control gets +2/+1, and the opponent has already lost the chance to respond to it with a block decision. That sequencing is the whole point of the card, and the "must be blocked if able" clause is a separate lever pulled after the pump has resolved. A 4/2 for is priced to swing, not to trade, and the compulsion is narrow: a defender only has to commit one blocker to the Brawler, not the whole board, so this is a taxer on their combat math rather than a true lure that empties their defense. You force one creature to eat the 4/2, the boosted Elf swings alongside it at +2/+1, and the rest of their blockers now have to cover a stretched-out attack with one fewer body available. The Brawler dying in the block it forced is a feature, not a cost: the pump already happened, so a creature built to be spent plays cleanly with recursion and sacrifice value. The real weakness is legibility. With no second Elf on board, the attack trigger has no legal target and the "must be blocked" clause just staples a liability onto a fragile 4/2 that folds to almost anything. This is an Elf-count payoff, not a card that stands on its own rate.