Slime Portals are a simple game mechanic. They consist of a large player sized portal from which slimes of the same type emerge. They seem to be random, but have some comedic timing. This humor however can be fairly dark.
When and where they can appear
Portals consisting of only feral slimes or tarr may appear if the player is at 10 or less health
A portal with a single gold slime may appear if the player's inventory has no food and at least 5 items in each slot.
If the player has a slot full of a slime type, a portal containing solely that type of slime will appear
Slime portals can put types of slimes directly into incinerators, especially gold slimes and chickadoos (you will not get the you monster achievement).
Slime portals can give you a single lone chickadoo for no reason whatsoever.
Slime portals dispense plorts into the plort market, but of course this money does not go to you.
Slimes may be dispensed directly into the sea if you have been collecting that type of slime unsuccessfully.
Rock slimes can be dispensed at very fast speeds straight at your face.
Boom slimes can come out of the portal a fraction of a second from exploding.
Slime portals can appear in the vacpack, to give you various items.
Slime portals can appear under tarr to send them to the other side of the portal.