Shadowverse

it's enough for her to summon a follower stronger than 2/2
and that's already a profit.

Committing to a suicide play for five mana against a 4-mana creature with 4 damage (Pop, Floralka, Elf, etc. - common in Constructed, less frequent but still common in Arena) isn't valuable. And you can get a free Lich much easier, without evolution and one turn earlier - with the help of Ur'd, and you'll still have a unit left to give another Lich later, and in terms of stats, the evolved Ur'd (for comparison) for 4 mana will be even better than Ceridwen.
In short, it's a unit without a clear purpose, only useful in Arena, for specific situations that happen rarely.