What is the fastest way to get 100 mythic cells of one mythic cell in Monster Legends without spending money or too much time?

I went back to this game I used to play today, and I only have one legendary as well as no mythics. The only way to get mythics is by crafting them with mythic cells, or getting them on the challenge pass thing, which requires a super high level which takes so much time. The most of one that I have is 20 from a maze. Without a mythic, PvP is hard (especially against players with mythics)

I do not spend any money or more time than 30-45 minutes per day (usually, I’m quite busy).