Reference

Gelatinous Champion

Gelatinous Champion The ability: High Sacrifice, Gives 3,000 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

High 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 5%
Hire with Shards 150 Shards 100 %

* -Chances are approximate.