The only thing to fight back Horus 99% stun chance is angel talisman on a cleanser like the Alchemist.
There is this talisman set that removes 2 buffs from each character, I think it's called redemption or something like that. Well, that plus Horus equals no mercy punishment for teams without angel.
Got a taste of that yesterday, I don't have angel, so I go with vanish or immunity and hope for the best. This defense took out 2 buffs from each of my guys, leaving my team with zero immunity (I had trap set, so at least that fucker was stunned, lol), ok fight starts and here comes Horus and BAM my guys all stunned, the rest of his team did some damage but nothing too heavy, my turn... I wish, all my guys stunned and beat up so back to him, second turn and guess what... Horus and his amazing 100% accuracy strikes again and that was it. Didn't have the chance to do one single move. This happened to me a few times, frustrating as fuck. Gotta find me one last angel talisman to complete the set and defend myself from Horus amazing 99% accuracy.