New Order could be used to create a seal. Unchange beat Andy with solidified air, a trick SaS can do too. Undead's regen can also be negated. We know this from his interaction with Unrepair. She'd need his name, but "your body will not mend", should be enough to turn off his regen. Billy would need to put the work in to get SaS to view killing him as moral good (Justice) so that Unjustice could flip that goal into self termination. This might actually be super easy. Billy already has to be an S-Class dbag in order to steal powers. He knows how to roast his enemies just right (like he did Ruin), and the cap/mask combo make SaS an easy read. Lightspeed required that Unstoppable loop the planet. Billy also doesn't have Unbreakable's armor, so he's going to need to regen, like, his whole body after any LS attack. Unmove + Unchange is probably the GOAT combo here. Unmove can be pretty trash without good synergy, and Unchang is perfect synergy. Or... maybe not. When Billy first...