Starting the Quest
To start the quest, you must speak with Grendel the Really Old. If you haven't already completed the first Magician Quest, you'll have to complete that before moving on to the second one. You can find Grendel in Ellinia's Magic Library. Ellinia is located on Victoria Island. To get there, select it from the Victoria Island map.
Finding the Slimes
Grendel the Really Old tasks you with defeating 20 slimes. It doesn't matter what color the slimes are, so unless you want to challenge yourself, you can focus on easy ones. As it turns out, a large population of slimes lives right by Elllinia. To get there, return to the Victoria Island map and choose the location immediately to the west. Here you'll find more than enough slimes to complete your quest.
Killing the Slimes
Slimes are particularly weak against lightning, and since you're now a Magician, you might as well use that weakness to your advantage. Fling the spell Energy Bold at them to take them out quickly. If your character is strong enough, he'll kill each one in a single blow. If you run out of mana points, run away from the enemies and wait for a while. Your mana will gradually replenish on its own.
Completing the Quest
Once you've killed at least 20 slimes, return to Grendel the Really Old. Click on him, and he'll congratulate you for completing his task. Your reward is 30 orange potions, 30 blue potions and 323 experience points. Orange potions restore your hit points, while blue potions restore your mana points.
Max Level
Since this is a training quest, it's meant for low-level characters. If you reach level 30, then you will not be able to accept or complete this quest. Because of this, perform the training missions as soon as you can. Otherwise, you miss out on an opportunity for easy experience and a good number of potions.