This is the third boss in the game, which guards the Lab Coat.
Uruku has an annoying hit box (its mouth) and a number of troublesome attacks that can turn this battle into a slog. An easy way to beat it is to destroy the first mortar pustule (the bottom left purple orb on the boss) from the relative safety of the left side of the arena. Then, jump into the lava (it drains your health as you remain in it, so keep jumping to minimize damage) and use the Address Disruptor to make two sets of blocks appear underneath the pustules. Jump on the blocks that appear under the remaining pustule and then destroy it. With the pustule out of the way, aim up diagonally to the left and you'll have a clear shot at the boss' mouth and you won't be at risk for damage for the rest of the fight.