Assist Trophy Suggestion: Buzz Bomber from the Sonic the Hedgehog series
Buzz Bomber would be a pretty simplistic assist trophy, when spwaned, they would fly around the stage horizontally, shooting off small projectiles from their "stingers", they can also fly off the screen, if they do they fly out the other side a little bit higher.
If KO'd, they will explode and one of the animals from the Sonic series will pop out and quickly flee the stage
As for why they should be included, they are one of the most iconic enemies in the Sonic series, and their inclusion would give some love to the various robots in the series, an aspect that has been ignored even by spirits, and in the event Knuckles or Shadow are promoted the Buzz Bomber would be a suitable replacement, especially since they're not a character people want to see playable, meaning no one would be upset over their inclusion as an assist