For Unicorn chomper, this's the only way to get master it and reach Max rank on GW2 so this's how Popcap listen to community request and fulfill it. I mastered it in no time.
For legendary/party, it's how popcap advertise by let people try it out before commit to buy it or grind it to get it. Some people/kid doesn't have money to spend so they might simply grind all 4 days to mastered all of them. It's a lot of works and a lot of time but possible. I mastered 2 characters in 1 day (Unicorn and disco Chomper) since chomper is one of my favorite character. now I officially master ALL my chompers!
Next, I'm going to grind on Z7 and Scallywag Imp to master.
Note: I was also surprised that they're not too many Unicorn on this event, I guess many people already mastered it from previous event (lunch at lab).