Big Icedus
From Sonic Retro
Big Icedus (ビッグアイスダス), the boss at the end of Icecap Zone Act 1, is a small machine that looks a little like a gray snowman who summons eight snowballs to swirl around him. At the beginning he is, alas, out of hitting range (even when using W Kaiten Attack) unless you have a lightning or water shield.
After he surrounds himself with snowballs, he swoops across the screen twice; stay in either corner and you'll be safe. Then stand below him and wait for him to release his snowballs. Then jump and hit him, preferably twice, before he moves up out of hitting range. Then comes the tricky part; five of his snowballs fall from the sky once, and you must slip in between them to avoid getting hit. They fall quickly and without warning so you must react quickly. After this he repeats the pattern, sometimes swooping across the screen once instead of twice. Keep hitting him after he releases his snowballs. Six hits does him in.
Aside from the variations to the attack pattern, this boss is very reminiscent of the Metropolis Zone boss from Sonic 2 in that it protects itself with a barrier made of several "spheres" (in this case: it's snowballs) while trying to ram into the player.