Hotarion

There are two Hotarions in the Mega Man X series:

Mega Man X
This Hotarion will light up a space whenever Mega Man X is walking. It only appears in Spark Mandrill's stage. He is very fast in the entire stage, so X can't return and get him after he goes away. X will notice that it cannot only help to light up the blackout, but it can harm him.

Mega Man X Collection
This Hotarion appears only in Izzy Glow's stage and the final stage. There are two attacks from him. One materializes and fly in the direction of Mega Man X or Zero. Another one will float high to make a wall of lasers. This is also the firefly that appears with the F-Laser.

Trivia

 * Hotarion comes from the word, "hotaru", which means "firefly" in Japanese.