The Giant Sponge Monster is a one-shot villain who only appeared in Speak No Evil.

While on a trip to Japan, it was given to Tuck by Jenny as a gift in the form of a tiny green capsule-shaped sponge creature. Tuck mixed up the instructions that stated to expose it to sunlight and not to water it, and mistakenly got the tiny spongelike capsule wet. It absorbed the water and expanded; terrified, Tuck continued to spray it with a water gun until it grew into a massive monster. The spongy monster then rampaged in Tremorton because the water caused it pain. Fortunately, it was helped and placated by Jenny when she rung the creature dry, reverting it to its original state.

Later, at the end of the episode, Brad was given a similar purple creature that reacted negatively to sunlight as opposed to water...