The Portal is the entrance to The Bad Place. It is found in Anatat Tatanatat, after you have passed through the exit in Temple of Gloom and accessed The Bad Place. When you exit the level, the Portal will re-appear.
The Portal also appears in the Fluffmatch, Fluffraiser. However, this Portal replenishes Health Points, and will continue to push HP past 100 should you remain underneath it. Like with Super Pet Yums, HP gained this way gradually declines until it reaches 100.