I have a level 306 Professor X and I struggled. I dunno how you managed with a 3/1/1! Congrats dude =D
Remember to be careful about when you go invisible. If you can avoid it, don’t do it when there are available purple matches on the board, or you run the risk of the computer immediately matching it the next turn and wasting (usually difficult to collect) purple AP.
I’m finding it especially hard since I haven’t been able to get a board that produces purple tiles. If I’m lucky there will be enough at the start to get my invisibility up but since no (or very few) purple tiles pop (and with Elektra doing Shadow Step all the time) once my invisibility tile is match I’m a sitting duck.
I remember this being a dreadful crash but managed to win first try with +1 purple boost and a lv100 5/5/3 Prof X.
Key to success was to equip a support, Element Guns did the trick - fortify that Invisibility tile and watch Elektra throwing a fit 
LT to the hoard until Loki leaves Latest.
True but even general chat has limited activity the other boards are bound to have less
Lost first try.
Came again with +4 purple and won easily.
Need to get invisible ASAP, hit as many of Prof Xs colors once she gives you strike tiles, then block her purple and/or kill her before she can turn them around on you.
I think this one stands out as sub-par because it is really luck based. Get a match 5, and you’re fine. If your invisibility tile lands in a manageable corner, you’re fine. Just deny black and keep boosting strikes. But if your invisibility lands where it is easily matched, you get messed up pretty quickly.
One of the odd things about this one is that the difficulty doesn’t really change much. Regardless of level or coverage, it pretty much just comes down to getting Invisible and staying that way. Anything else is just a bonus.
You kind of want her to spam with her stupid Purple move at least once after you go invisible, to give you some very low end attack tiles to boost each match you make and do more damage. After four or five rounds of those boosts, you’re dealing a couple thousand with each match, and no matter how many times she shadowsteps, it’s a matter of time before she slips up and is knocked out of the match.
So I see a couple variations on “this is an easy fight/just stay invisible” and I think some people are missing my original point. I specifically said this isn’t an unwinnable fight but that it requires significant time/luck. PX has only one active power and it doesn’t do any damage meaning you’re relying almost exclusively on match damage to win. Which would be fine if not for Shadow Step which allows Elektra to dodge your damage and deal damage back. “Just stay invisible and wait it out” I hear you saying, but are you forgetting Ballet of Death, which let’s Elektra steal AP and, again, deals damage. The point is that win or lose this fight is an unenjoyable slog.