From Teletraan I: The Transformers Wiki

A list of characters that have physically travelled from one continuity family to another, or from outside the Transformers multiverse to inside the Transformers multiverse, or vice versa.

This list does not currently include characters that have time-travelled or moved from one dimension to another within a single continuity family. The list also does not feature characters who were drawn from their own dimensions to the Cauldron, a dimension contained within Unicron himself during Universe, a place not belonging to any specific continuity family.