Geode

Geode is the prismatic tank, crafted around the Mushroom Forest zone, and at 1 in 3.11 million it is the wall you bring to fights that punish glass cannons. Tier S confirms it is not a stepping stone, because Geode holds its slot deep into the late game without the kind of replacement pressure that flushes lower-tier tanks.

Pair Geode with a boss-killer like Stormy so one slime survives while the other deals damage. The pair rounds out the prismatic team that Ninja and King already started, and after Geode lands you have a complete loadout that handles burst, bosses, support and tanking without compromise. Until you reach the transcendent tier, this prismatic four-slime team is the strongest thing the game offers.

If your runs end because you die rather than because you are too slow, Geode is the fix. By the time you are routing toward Pokey or Bucky in the transcendent attackers, Geode is still in your active loadout because no prismatic or transcendent tank is cheaper. Until Pumpkin shows up many tiers later, Geode is the wall.