Croagunk resembles a dark blue bipedal frog, with a white band around its waist area and red and black markings on its hands and feet. Its coloring and poisonous nature suggest that it is based on poison dart frogs. The markings on its body make it look like a Muay Thai fighter, and its jutting teeth make it appear to be wearing a mouthguard. The black around its eyes and the white bands make it look like an injured fighter with black eyes and broken ribs. Its cheeks are filled with a poison that runs to its fingers, allowing it to poison opponents by stabbing them.
The two white stripes that run across the female Croagunk's abdomen will be higher up than the male. The black part of the female's hands are also larger than that of the male's in Platinum and HeartGold and SoulSilver.
Whenever its middle finger glows purple, it appears to be channeling its poison via its skin and onto its hand to use its Poison moves. Fluid squeezed from its finger, although poisonous, is a significant ingredient in remedies for lower-back pain. Croagunk can have the ability Anticipation which makes the Croagunk shudder if the foe has a super effective, instant KOing move, or a move like Selfdestruct. Croagunk may also possess the ability Dry Skin, allowing it to heal itself during rain or when hit by a Water-Type move.
Croagunk are generally mischievous and mean. A few Croagunk, however are more comfortable being alone, simply staring at the views around them. Croagunk may also make noise by expanding its poison sacs.
Croagunk live in moist areas close to bodies of water, such as swamps and marshes, or forests where there is very little light.
Croagunk is one of few Pokémon to have its hand-held game sprite differ from its 3-D image. While in Pokémon Diamond, Pearl, and Platinum it is shown to have pink cheeks, its 3-D models, official artwork, and anime appearance show it with yellow-orange cheeks.
Despite having "gunk" in its name, it can only learn Gunk Shot through the move tutor in Platinum.
In Platinum, in front of the PastoriaGreat Marsh, if the player stands behind the Croagunk Wall with the his/her head sticking out of it a wild Croagunk may come by, cry out, and then walk to the Great Marsh.
Being based on a frog or a toad, it is unable to learn the move ''Lick''
Croagunk is probably a combination of croak and gunk.
Gureggru may be derived from ケロケロ kerokero, the Japanese onomatopoeia for a frog's croaking, and げろげろ gerogero, the Japanese word that's used to describe something disgusting. It may also be derived from 汚れ yogore, filth.