After you get all of the 100 slimes and defeat the final boss (Flucifer) go to Mt. Krakatroda's east tank arena. Instead of the usual boss it should be Slival.

Fight him and win (his tank starts with 3000 HP). If you do win you will be rewarded with orchalslime and access to the Swarzman tank in Morrie Morrie's tank masters tournament. You can only access the tournament by getting 55 slimes or more and Morrie Morrie. He can be rescued from a tank battle).