Reference

Crystal Ooze

Crystal Ooze The ability: Mid Sacrifice, Gives 600 Skill EXP when sacrificed.

Slimes can’t be used in battle. Instead, they’re used to increase your Heroes’ skill levels.
Hero Altar – Consume any Sacrifice

Mid Sacrifice

Claim

Hire more powerful Heroes at the Hero Altar!
Switch your Heroes Altar to Item Mode to store hired cards and essences in the Warehouse.
You can hire Heroes by spending Shards, Gems, or Honor.

Hire Hiring Cost Chances *
Hire With Gems 150 Gems / 450 Gems 21.9%
Hire a Hero using HB. 500 Star 2%
Hire with Shards 30 Shards 100 %

* -Chances are approximate.