It's possible to attack an Untouchable minion, if the attack is initiated before the minion transforms into one

[Jetz72]

https://us.forums.blizzard.com/en/hearthstone/t/dormant-minion-attacked/29303/

I was playing against a rogue as a DH. I was attacking a 2 Cost minion with my DH, when the secret Bamboozled was cast. Therefore the 2 Cost minion was transformed into a 5 cost minion. In this case, imprisoned Altaen. I still attacked him although he was dormant and got 10 damage to my hero, while he didn’t get any damage. Is that supposed to be that way?

https://www.reddit.com/r/hearthstone/comments/fwsdzh/bamboozle_bug_took_the_10_dmg_attacking_into_the/

Bamboozle Bug? Took the 10 dmg attacking into the Dormant Antaen

Haven't tested yet, but I haven't heard of this happening with Duel or Wild Bloodstinger, so I'm guessing you can't initiate an attack against an untouchable character even if forced on a specific target. You can only carry it out if you begin it before it enters that state. If so, then I can't think of any reliable way to reproduce this without luck.

In any case, untouchable characters probably aren't meant to be involved in combat. Attacks should presumably abort like ones ones with dead combatants do.

[Jetz72]

https://twitter.com/Celestalon/status/1248839323572527106

Yeah, Bamboozling into a dormant minion should abort the attack; we're working on a fix for the next major patch.

[Jetz72]

Still being reported.
https://us.forums.blizzard.com/en/hearthstone/t/wandering-monster-dormant-bug/33345

If you have the secret Wandering Monster, and it summons a dormant minion, the enemy minion that attacked will get stuck in the attack position until it does another action.