@Neko Majin C  
You do realize you get her for free as she the main reward for the event and get extra 10 upgrade tokens.

I really do not like the fact that the Minotaurocellus’ do not give out upgrade tokens. The only way to keep the characters you find in the maze is to upgrade them and you only get upgrade tokens from the first Minotaurocellus and the tutorial forces you to use them all. Sure, you get them from Decepticolt and the two other ponies, but you only get ten from each of them, and it costs twenty tokens to upgrade a character. Which basically forces you to buy, with gems or real money, the upgrade token bundles. I have not yet gotten to Cosmos, but if she is the same as the other three ponies, unless she comes already upgraded, or she gives you enough tokens to upgrade her, if you have not saved at least twenty tokens you will not be able to keep her.

@Jacalope  
Oddly enough the most powerful character I had besides Twilight Sparkle in the last fight was a filly with 107 power, Cheerful Student or something like that. I was really surprised that Cosmos was not a lot tougher than she was; I expected I would have to backtrack and buy some high-power characters but I only had to buy 2 in the whole game.

Imagine put all the draconequus like helpers, you have all the game won.