So basically I have been inactive from this game up until recently when Mercenaries was active again and I started getting Skill Points for use in Pro mode... Can anyone clear this up for me?
You have to participate in the RE.NET events that will give away tickets for EX3 costumes. Just go to the website and see if any of the current events will give you a ticket for an EX3 costume. I can't remember if any of the current ones are doing that now. I don't really care for them.
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Most of the events just reward RE Points for participating, which you can use to customize your page and buy EX2 costumes. The events usually have tasks like speedrunning a certain chapter or getting a high score on a specific Mercenaries stage.
The EX3 events seem to be at the beginning of each month, and as long as you fulfill one of the objectives, you're considered to be participating. They seem to focus on killing a certain type of monster.
The "Pax Aeterna" event starts in two days or so. As long as you kill Deborah in Leon's story at least once this weekend, you should get an Extra Ticket when the event is over. The ticket is used to buy the EX3 costumes.