Shiversaw is the fifth mini-boss fought in Sonic Mania, encountered at the end of Press Garden Zone Act 1. It is a floating machine wielding two circular saws on extendable, rotating arms. The unit at the front of the machine - presumably its engine - somewhat resembles a face.
The saws are on arms that can rotate to face the player's position, thus protecting the machine from normal attack. Stand near one of the orange crates in the room, and the machine will wind up an attack. When the attack launches, dodge away and the saw arm that is extended will shatter against the crate it hits, giving a brief window to attack before the saw is replaced. There are also a limited number of crates in the room, so the player must use them wisely. The machine can be hit while under the effects of mercy invincibility but this is not guaranteed to work.
Defeating Shiversaw will cause the entire zone to freeze over, revealing its true beauty in Act 2.