Linvala, Shield of Sea Gate
A 3/3 flier at this cost is a fair body on its own, but the combat trigger stays dormant until you have assembled a full party: a Cleric, a Rogue, a Warrior, and a Wizard on the board at once. Meet that condition and every combat step becomes a lockdown, marking one nonland permanent an opponent controls so it can't attack, can't block, and can't activate abilities until your next turn. The activated-ability clause is the sharp part, because it reaches past attackers to shut off planeswalker loyalty, tap-effect mana rocks, and any activated combo piece. Assemble the party and the tempo swing is enormous; fail to, and the trigger does nothing, which is the tax the deckbuilding pays for the effect. The sacrifice mode is the second half of the design and the piece that turns her from a fragile enabler into a control finisher: cash her in for team-wide hexproof to dodge targeted removal, or indestructible to survive a wrath, at instant speed. As an Angel Wizard, she counts herself toward the party's Wizard slot, a self-referential touch that keeps the four-class requirement from feeling like a separate chore. The build she wants is a critical mass of small creatures spread across the classes, precisely the go-wide board the sacrifice protection was designed to shield.
