We're going to start with some hard numbers (brought to us by Frank Karsten, because despite his description of "basic" I have no idea what hypergeometric formulas are - hey, I'm a musician, not a mathematician!), then talk about reasons why we might adjust those numbers some based on goals, play styles, and desires
Absent green, it's just unplayable
Activate only once
I'm going to need a bit more than one free creature to exclude half of the cards that I want in my deck to play this six-drop when I could just play Liliana and be done with it
Here are the cards you need for 'Eevee Grove Museum': Flareon ex #87 (Rainbow / Two Gold Star) Primarina ex #88 (Rainbow / Two Gold Star) Sylveon ex #89 (Rainbow / Two Gold Star) Dragonite ex #90 (Rainbow / Two Gold Star) Snorlax ex #91 (Rainbow / Two Gold Star) A Sweet Party of Epic Proportions The 'A Sweet Party of Epic Proportions' Secret Mission tasks you with collecting 100 of the Milcery card from the Eevee Grove booster pack
For long-term appeal, Pikachu, Mew, and Eevee-related cards continue attracting strong demand from collectors worldwide.