Your character and mount both turn green when summoning Disgusting Oozeling.
Now, this one is not easy to farm but here are some tips found in Wowhead > Source
This pet can be found in a bag with a 1.5% drop chance only. The bag itself is difficult to get, drops from several mobs (1 to 10% depending on the mob.)
At the starting area for DK, a player found a spot full of these mobs with a 10 to 11% drop chance for the bag. They despawn if you complete a certain quest so be sure to read the comment in Wowhead.
To make it simple, you need to create a DK and start some quests then go directly to the spot and farm these bags. It took me roughly 2hrs to get the pet but it’s a good spot I think.
Whatever you decide good luck, also don’t hesitate to leave a comment below!