Platinum Emperion

The lock-down stated in absolute terms: not "you can't lose life" but "your life total can't change," shutting the door on both halves at once. That symmetry is what makes it more than a hexproof-on-your-face effect. Burn does nothing. Drain does nothing. But so does your own Phyrexian mana, your fetchlands, your Bitterblossom, your Necropotence draw engine, every effect that asks you to pay or shock yourself. It is a creature that taxes you as hard as it protects you, which is the design tension that keeps an otherwise unanswerable shield from being free. The 8/8 body for is colorless and clean, so the prerequisite is just having eight mana and a deck that has already made peace with never paying life again. Functionally it freezes your life total at whatever number it was when this resolved, which turns the entire race into a wall: until the Golem leaves, opponents cannot drop you a single point, so combat and burn alike stall against a total that simply won't move. The closest cousins in concept are the various "damage can't be dealt to you" enchantments, but those leave drain and life payment untouched while still letting your own total drift; this one freezes the number itself, at the cost of freezing it for you too. Note the limit of the lock: damage is still dealt and still tracked, so anything keyed to damage rather than to your life total reads right through it. A card built for the player who has decided their life total is no longer a resource worth spending.