Roto-Disc

Roto-Discs are firebar-like entities that first appeared in Super Mario Bros. 3. In this game, one or two Roto-Discs are found circling gray orbs, on which it is possible for Mario or Luigi to stand. Roto-Discs are nearly invulnerable, they can only be destroyed if Mario or Luigi transform into a statue by using a Tanooki Suit and land on top of one. If there are two discs orbiting one orb, the player will only need to destroy one and the other will disappear.

Aside from Super Mario Bros. 3 and its subsequent remakes, the only other appearance of Roto-Discs is in the Mini-Mario course in Bowser's Castle in Mario & Luigi: Superstar Saga. As a throwback to the previous games, they are obstacles that can defeat Mario in one hit, sending him back to the beginning of the area.

Trivia
In Super Mario Land, very similar enemies that are possibly Roto-Discs orbit a similar locking block and share the same attack Pattern.