8. Android 18
Outside of Android 17, the only reason Captain Ginyu and Nappa's underlings have remained under the radar, is down to their clunkiness and situational usefulness respectively. It's best they stay that way, or else we could end up with more overtuned examples like this.
But then, that's the inevitable danger of allowing characters in a tag-team fighter to call upon un-punishable, invincible assists, especially when the contentious example in question is an integral part of a character's toolkit. 17 provides more utility than the stock assists that every member of FighterZ' cast has access to, and they're just as susceptible to damage as their wards, so why is 17 the exception?
If anything, his purpose as a combo-extending maniac should warrant that he has his own individual health gauge to account for. As is, the reformed villain brings too much to the table for him not to allow any sort of counterplay.
Either lump 18 with a cooldown that bars 17 from frequent, repeated entry into the arena or take away the invulnerability. It's time to play by the rules.