So, how are you liking Dr. Strange? I know you were really excited about him, and he looks like a really different hero with all his spells. I hear his spells look awesome, too.
You can use team-ups anytime you want. You can either keep them out permanently or use them as 30-second summons that are more powerful (since they're only out a limited time), or you can even not summon them and get passive benefits from them.
Did you redeem that MHMGIFT code today for the free 200 splinter hero and boosts? I happened to get lucky and get the only 200 splinter hero I didn't already have, which is Thing. I haven't gotten around to playing him yet, since I was checking out the Panther review, but that's pretty cool!