Time portal

Possessing the ability to transport people and objects across space and time without involving the mass substitution process, the time portal is a powerful and dangerous piece of technology. When used improperly, it can have catastrophic consequences for the universe.

Fiction

Marvel The Transformers comics

Reduced to a disembodied head by the power of the Matrix, Unicron came to rest on the planet of Junk where he mentally enslaved the population to do his bidding. As well as a new body, he had the Junkions construct a time portal through which he would be able to punish his errant creation Galvatron. Though Unicron's plans were ultimately thwarted by the intervention of Rodimus Prime, Wreck-Gar, and Death's Head, the time portal was operational long enough for the bounty hunter to throw himself, Cyclonus, and Scourge through it to escape the ensuing explosion. The two Decepticons ended up serving under Scorponok in Cybertron's past, but Death's Head completely disappeared. The Legacy of Unicron!

Notes

• It was because the time portal bypassed the mass substitution process that usually accompanies time travel that the time rift was created, as seen in "Space Pirates!" and "Time Wars". Considering that the portal's designer had the ultimate goal of annihilating all life in the universe, this may have been an undocumented feature.
• If Unicron had retrieved Galvatron from the past, would Skids have remained trapped in Limbo forever?