From Trickster Wiki

What are Hardants?

Hardants are compound stones for pets, instead of equipment.They are purchased in myshop in varying levels, stat type, and prices. Only one hardant is needed in each available slot. Only certain types of hardants could be equiped at certain pets, like normal equipment. Equiping a hardant to a pet will serve to boost the stat of the pet depending on the type of the hardant equiped.

How to Equip a Hardant?

Talk to Pet Trainer Shara to equip a hardant into a pet. Pet Trainer Shara could be found at Megalopolis Shop and Paradise Shop. Like mature compound, the amount of stat increase is based on a number to number range. However, unlike maturing compound, there is no (known) way to increase the chance of getting a stat boost in the high ends. It is assumed that it is based in real luck, not in-game LK stat.

I'll put some pictures when i learn how it works ^^