Mfw I suggested Kessler vs Mami way back when
Anyway, Phantasms and Memory Inject are probably Kessler's best bet here, as most of his other stuff gets countered pretty hard
Stat amping and regen counter his AP, regen null counters regen (duh), bypassing attacks will bypass his shields (again, duh), and she can reflect his attacks back at him.
Though, his durability and endurance may help him out, as he was able to withstand a bunch of attacks from a pissed off Cole, who is ridiculously high into M+, and could with stand his Lightning Storm for a bit, which is many times stronger than his normal attacks. But I think her flames may counter this as well.
However, she won't know that touching the clones will cause mindscrew, so he has the advantage of surprise, but they're really slow, and she usually uses ranged attacks, doesn't she (haven't watch PM, despite my friend bugging me to). However, Kessler doesn't just summon the clones and lets them do all the work, he also keeps on the pressure with his ranged attacks, so he could possibly distract her long enough for one of the clones to get the drop on her, or use his clones and summons to distract her enough to get up close and memory inject.
What's her telekinesis and lifting strength like? Cause it may be possible for Kessler to rag doll her into one of his clones of he needs to.
Also, paradoxing is an option.
Also, what's going with speed? Equalized or nah?