It's hard to top what you've already written. Adding extra charges is especially hard since the ones you currently have were deliberately set up by you in advance (your vandalism charge only works because you had the foresight to summon a flesh horror). Those are always going to be superior to ones added retroactively. The only additional charge I can think of is adding Child Abuse (perhaps one of the demons was actually underage).
I have some ideas for the coutroom though, especially in terms of ways to mount an effective defence.
Jurisdiction Conflict: For a court that prides itself so much upon the letter of law, it is astonishing that the infernal court is willing to overlook the plaintiff's blatant interference in the legal proceedings of another sovereign plane. His actions very well may have caused a mistrial! *shocked gasp from devlish jury*. Doesn't he know that Hell has an extradition treaty to prevent these kinds of incidents?
Hiatus in Anticipation of evidence: I don't know the official legal term for this one, but in some courts if a client has multiple pending trials, and if it's likely that the outcome of one trial will significantly influence the subsequent trial, then that trial cannot proceed until the previous one has been concluded. Since so much of the clients' defence rests on whether or not the plaintiff committed harm, the outcome of the trial in the material plane plays a pivotal role in the outcome of this one and this trial must be postponed till the former's conclusion. Tempt the party into sabotaging their material trial to improve the odds of the hellish one, only to have it be undone by...
The Plaintiff's Paradox: If the Plaintiff's actions cause the client to receive a guilty verdict, then we can conclude that the Plaintiff committed
harm, thus we must give an innocent verdict, thus the plaintiff did not commit
harm, thus we must give a guilty verdict, thus the plaintiff did commit harm, thus we must give an innocent verdict.... etc. This can be a defence or an attack defending on where you stop the recursion.
I summon the witness!: While we try to determine whether the plaintiff's actions negatively impacted the outcome of the previous trial, it may be useful to ask the jurors themselves how the demonic invasion affected their perception of the clients' innocence or guilt. Let me just finish drawing this pentagram and- Wow! didn't expect so much screaming... do they really hate the wallpaper that much? (Feel free to do the usual witness badgering, ask leading questions, etc. For extra fun, use the power of prophecy to summon people who were only supposed to become jurors in the future. If you want to go even farther, you could plane-shift the whole town into hell for the duration of the trial.)
Multiple Hearings: We have exceeded our allotted time and the judge believes there is not yet enough evidence to reach a verdict. For the time being, our client will be released on bail and will return to court when a slot will next be available (I don't think there's anything that screams legal hell more than a protracted lawsuit. Plus it gives you an excuse to let the party go back for adventuring. For extra torture, make them pay bail after each hearing and continuously increase its price).
Ultimately, I think a hellish court that tricks the defendants into thinking that they actually have power over their verdict is better than one that's blatantly kangarooo from the outset. It would go a long way to boost player investment if the defence lawyer could actually get some of the misdemeanour charges dropped, and let the player's actions decide how badly they fumble the breach-of-contract defence.