Kolobok is a monster from the Russian folk tales. It is a roundish piece of bread that gained life and went in a forest to wreak havoc and terrorize animals.
This one is much more massive than a usual kolobok.
Katakana "go". It's a reference to JJBA menacing/rumble sfx.
Cool stuff, now I wanna fight Kolobok! What is the Japanese character to the right that's repeated a bunch?