As the name of the Badge suggests, you will need to meet the Owner of the Game, Infected Developer.
This is pretty hard as the Owner joins the game rarely. We also don’t know when he will join it. Upon joining a server of the game with InfectedDeveloper in it. You’ll get the badge and also to Access the MiniToon Morph. There is a Way to get the MiniToon Morph without getting the Badge?
First, you’ll need to Open your inventory and get “Billy’s Drill” and “Bunny’s Crossbow”. And then you’ll have to enter the Gamepasses room and stand beside the wall.
Once you’re here, face the Wall and keep walking while spamming Billy’s Drill and Bunny’s Crossbow.
Make sure not to Touch the Purple Wall as that’ll make you go back to spawn. 
Now Simple Step on the Pad to get the MiniToon Morph! 
To get out of here, simply use Billy’s Drill and Bunny’s Crossbow. 