If your a spender in this game, there is a fabulous one two combo right now.
I'm sure most of you are aware that you can get Kitty Pryde in the double track event. Kitty has been one of my favorite characters since the 90's and one of my all time (if not all time) favorite MCoC characters, so I was stoked when she was available. For the first time, I bought the progression boosters to get her day one and after I popped my unit crystals (the Deadpool ones) I had roughly 2,500 units (I'm not sure if this is good luck but I think its reasonable to assume most people will get nearish to this number).
In the "Tooth and Claw" tab in game, there is a 7 star awakening gem that works for her for 2,500 units. You can wait to get her over the next few months of course or use your gems if you have one, but if you don't have one, that was probably the most satisfying hundred bucks I've ever spent in this game (7 star Kitty Pryde + Awakening Gem+all the random stuff if the track event).
Just something to consider.
p.s. You can also put all those saga sig stones you get form Solo Colosseum into her aswell.