From Brotato Wiki
Elites
Elites are special enemies that only appear on certain waves. If any elites will spawn in a run the the player will be notified in the Shop. No elites will spawn in dangers 0, 1 or 2 but 1 wave can have an elite enemy on dangers 2 and 3 and a maximum of 3 waves can have a elite on it on dangers 4 and 5. If you kill an elite then it will drop a red crate with a guaranteed drop of a legendary item in side of it.
The Rhino
Mutation 0
(initial phase)
Slashes 4 times every 1.25 seconds around the player pointing to the player.
Mutation 1
(upon reaching 60% HP or after 25s)
Slashes 8 times every second in a random pattern around the player in a large area.
Mutation 2
(Upon reaching 40% HP or after 40 sec)
Slashes 3 times every 0.6 seconds around the player randomly in a large area that deals 33% less damage.