1 XP When you first wander into a scene in an already ongoing event, and you act as if nothing is amiss.
3 XP The first time someone enters into Buddy or Team affiliation with you, and they express their desire to actually work with you.
10 XP When you either decide that this group is exactly where you belong and everyone agrees, or you decide that this group is lame enough that it might sully your good name, and you leave.
And now some inspiration from everybody's favorite "reformed" mutant thief, a la Gambit #2:
I Don't Trust You In the Least
1 XP When you first state that an ally of yours can't be trusted, or when they say the same about you.
3 XP When you allow an ally to suffer physical stress or a complication because you let them take the heat from your mutual opposition.
10 XP When you dissolve your partnership with another character at the same time you cause them physical stress or trauma.
And let's wrap things up with some inspiration from Captain Marvel #3 (which might serve as a framework for event specific milestones in an event with time traveling as a theme):
Pretty Sure This Is Not Going to Jibe With the Butterfly Protocols
1 XP When you wonder if an action that you are about to take will cause damage to the timeline.
3 XP When you take reckless action regardless of the integrity of the timestream.
10 XP When you find a way back to your own time, and you either decide to return home, or forsake your own time to live your your days in your new home.
I really wanted to come up with some Milestones inspired by this week's Avenging Spider-Man, but it's hard to build a set of them around taking emotional stress from hearing about your Aunt's love life.