Ah right, the smart-yet-dumb supporting character whose goal in life seems to be keeping Lord El-Melloi II's blood pressure higher than healthy (and giving him a target to practice his face-crush maneuver). Considering what he did to Trimmau, I don't think letting him near Chaldea's systems is a good or safe idea.
probably not. not familiar with the trinamu incident but he's also the master of a unique version of Jack the ripper in Strange fake.
Summoned from a mock up of one of jack's daggers that el molloi wone for beating a Video game, and accidently summoned him by connecting a circuit to the dagger in a park - no circle or incantation. fortunately, this Berserker jack is Sane and rational on acount of the madness countering is own mental state. he has no fixed form as is basically the combination of all the theories of who Jack was, able to take any of their forms and skills. he could possess Flat when necessary, and his NP's were the ability to turn into a demon and the power to become up to 200 individuals. His unstable form makes me think he'd need to manifest as a pseudo servant with Flat to manifest in a Grand order setting.
Flat's Chaos magecraft is so potent that in any timeline he doesn't meet Waver, the counter force has him assassinated. and he has skill with interfacing with other people's magecraft.
and of course he'd need babysitting from El Molloi