The Egg Frog (エッグフロッグ Eggu Furoggu) is the seventh boss of Sonic Advance 2, fought at the end of Egg Utopia.
This battle uses gravity switching for a tough boss. This boss is basically Eggman's Eggmobile with long legs. He uses these legs to leap between the ceiling and the floor. When he does, he drops a bomb that leaves behind a flame trail, forcing the character to leap to the opposite path or face certain death. Unique to this fight, pressing while on the ground and while on the ceiling will flip the gravity in your favor, so use this to hit the Eggmobile when it jumps to the other side.
Sometimes, the Egg Frog will slow down, causing it to move off-screen to the left before sliding back on-screen at the opposite surface in an attempt at a surprise attack on the player, so they must watch out for that.
The usual 8 hits (6 on Easy) will put this boss out of commission. Upon beating this boss, the boss rush level XX is unlocked.