Tyrant Guard

Ravenous and Shieldwall pull in opposite directions, and the tension between them is the whole design. The first ability wants X as large as possible: dump mana in, stack counters, cross the threshold of five to draw a card. The second ability then treats that counter pile as insurance for the rest of your board, converting the creature's own body into a one-shot protective spell. The catch is that Shieldwall is a sacrifice, so the fatter you make this thing, the more you pay to give it up. That is the friction the card lives on: it is simultaneously the biggest counter target on your side and the button you press to shield everything else that has counters. Shieldwall only defends creatures already carrying counters, so the effect assumes a +1/+1 shell around it rather than propping one up. Left alone, it is a growable green beater with a stapled-on protection button that blanks a targeted removal spell or a board wipe for a turn; surrounded by a wide counters board, it becomes a sacrifice-fueled hexproof-and-indestructible answer to the removal you most fear. Tying the reactive half to a permanent rather than a card in hand means opponents can see the threat sitting on the table before they commit to anything, which is the price of getting a protection effect that also swings for whatever X bought.