Unfair? not really. It's not like the unicorn chomper is OP and unless you're using its warp it's just a basic chomper but just looks cool to show off.
Regardless you have a year to earn him and it varies on how long it takes as it depends on how many skip challenge stickers you can get and how good you are in general to earn coins during your matches. Only took me about 2 weeks to go from 104-313 though i did sink a lot of hours into that.
The best tips i can give are buy the 10K pack for your stars as you can earn 1, 3, 5, 7, 10 stars from them (sometimes none at all though but the same could happen from the higher packs) and another tip would be to not skip the super easy challenges that you can finish in less than a few mins
