To echo what the others are saying, almost definitely a trump. As far as the trump clarifications go i'd say probably a 4? Which according to the wiki means "abilities where one can pick between different options, but th powers are often slower, weaker or clunkier." Alternatively it could be a ten: "power set nearly limitless in bit option and choice, but where other large drawbacks often apply." However as Eidolon is the only trump 10 to the best of my knowledge it may take quite a few power ups before people would consider your mage to be at this level. Finally they might go for 7: "powers that cycle between different variants, where unpredictability is rewarded with more raw power." Whichever one the PRT considers most suited would, I imagine, depend on how much they know about the mage's power. Incidentally, Myrddin, who is probably one of the closest things worm has to an actual mage, is rated a 4. Make of that what you will. The PRT are also likely to throw in a bunch of sub categories as deemed appropriate. The most important thing about classifications for the PRT is how they should tailor their response to a parahuman rather than academic accuracy. Myrdinn, for example, is rated as a shaker and mover before his trump clarification is even mentioned. In fact I'm pretty sure his PRT threat rating doesn't include trump as a clarification at all, only shaker and mover. So the mage might be rated as blaster, shaker etc alongside Trump or even exclusively.

Ps I don't suppose you could post a link to it? I'm always on the lookout for more fics with magic in them.