Unlike other evolutions, you MUST have both of these at MAX level before picking up a chest to evolve.
You need Pummarola (small red heart icon) at level 5, and Silver Wind at level 8, then simply pick up a chest and evolve it into Festive Winds.
To make it even easier, if you have Queen Sigma you can buy any skill you want at the beginning of the round from the guy at the start, and choose Silver Wind and just use your 100 rerolls to get Pummarola.
For people who aren't familiar with the game, you must find AND open the coffin in Mt. Moonspell first to unlock Miang Moonspell. It is the small question mark on your map when you press start. You also must kill everyone around the coffin before being able to open it, so go here after leveling up a bit, as the enemies are stronger around the coffin. Then you must also survive 15 minutes with Miang Moonspell to unlock Silver Wind.
Hope this helps 👍🏾