The Egg Spider (エッグ スパイダー) is the fourth boss in Sonic Advance, which takes place in Ice Mountain Zone.
This fight is underwater, making this fight harder than the usual fights. Dr. Eggman will move around left and right on the ceiling, making a stop to make icicles fall. The player must jump on the icicles to reach Eggman and hit him, or to take in air when needed. As with all bosses, it takes a total of eight hits to destroy him, or six if in Easy mode. When the boss is defeated, the water level will decrease.
Of all the characters, Sonic has the hardest time fighting this boss as he doesn't have any special trick to be able to reach Eggman without the aid of the falling icicles (his Insta-Shield doesn't quite give him the range needed to strike, even at the peak of his jump). Tails has just as much trouble, although his ability to swim & fly makes this fight more lenient for him, as it gives him the ability to get air more easily. Knuckles has the easiest time with this boss, as his ability to tread the surface of water will let him stay at the surface for air & get in a few shots at Eggman. Amy is a close second for ease in this boss as her Piko Piko Hammer will give her just enough reach to damage Eggman without needing the icicles to reach him (provided the attack is done at the apex of her jump). She will still need to use the icicles to get more air, however.