With active collection (every 4 hours, about 5 collection per day. Not perfect collection as we still need to sleep), one usually can get 1.1 k maze coins per day. The major one comes from breed/hatch, each gives 50 coins.
With maze dungeons and happy hours (assuming your Monsterwood is still working), we can get about 25, 26k coins from 21 days. If we save all and only use in the last maze coin move discount (30%), we might be able to get Zimnyaya (costs 36k without discount). Unfortunately this is nearly impossible as no way we can finish all the moves in one hour.
I don't understand why SP is making this event harder and harder (coins per day requirement keeps increasing). Yes they want to sell maze coins to those spenders. But if they make it easier for everyone to be able to get good monsters without spending, some f2p players WILL SPEND gems to rank them up later. SP is losing the business in the end.