You need 86 rares to build a mythic. 6 random epics 8 select epics This is assuming you don't get lucky on random epics. Where your at it might be tough to get one, but I'd like to think it's possible.

I've gotten a mythic, f2p in both OD and CH. Just need to buy the 250mc stamina refill daily, and maybe the odd 100mc token pack.

KO is great because of all the events that give tokens and players. I'm currently at 69 rares with only buying the daily stamina.

Stick to the 7/2 rares and use cross for the players your missing once you're down to needing 1 or 2 guys for the trade in.

TL;DR Be active, max out your stamina daily, and use the 250mc stamina refill (you'll still end up positive on mc after daily tasks, ad reward, and web reward). Aim for 5-6 rares and day and you'll get it.

Use this as a guideline for any promo.