MACC arriving through a Time Portal.
A Time Portal is a form of portal used as a time machine. It appears in the 1987 cartoon episode Attack of Big MACC. Unlike many other portals, viewers are allowed to see through the portal to the other side.
MACC arrives through a time portal. When Krang reprograms him, he plans to use the Time Portal to bring an army of MACC's fellow robots into the Technodrome. However, Krang is defeated and MACC returns home through the portal.
The Time Portal also appears in the episode The Legend of Koji. Shredder uses the portal to travel back to 1583 and when they discover this, Splinter and the Turtles follow.