So, I hit him with Hypersonic Assault, making it so he can't deal damage, then flip him during this, that means he can't deal damage when he flips, right?
Or is he no longer a target, and so the card can deal damage?
Well, rethinking that plan.
He’s no longer a target when flipped and thus not impacted by cards like Hypersonic Assault.
Ah. This happened to me, too. It does thematically make sense that stunning him wouldn't prevent him from exploding, but it sure was an unwelcome surprise at the time. Now I know : )
You can prevent Borr from dealing damage with Ground Pound or Grease Gun. One neat trick is to get Scholar's Alchemical Redirection and Expect the Worst both out. This protects all of your heroes from Borr while leaving villain and environment cards exposed. You need an extra card play to do it, but those aren't too uncommon in Obivaeon mode. Making your heroes immune to damage does the same, but because he deals both fire and energy damage you still need a combo to do it. Examples include Immunization and XPW Haka, Heroic Interception and Leader of the Pack, or Flesh of the Sun God with Lead From the Front and Next Evolution.
What other cool strategies have you run into in Obivaeon mode?
Grease Gun shouldn’t work as it only stops targets from dealing damage which Borr wouldn’t be anymore.
Another fun trick is to use A Brother's Sacrifice, then ping Borr up to a ludicrous number of tokens and let him flip. That was how I discovered that if Borr kills another Scion in Phase One, a new Scion enters and immediately takes a full Borr to the face, and if that's enough damage to kill them too, the process continues.
Oh my... :D