Tainted world

Tainted worlds are spread across the multiverse and may or may not exist in any continuity Unicron has visited.

A "tainted world" is a world created (or possibly re-created) by the chaos-bringer Unicron where up is down, black is white, cats chase dogs and Vegemite is a snack food.

Unicron began to consume world after world, reabsorbing the energy that it had lost creating other tainted worlds, Transformers: The Ultimate Guide, p50

Notes

• The phrasing in The Ultimate Guide suggests that Unicron created these 'tainted worlds' prior to his imprisonment by Primus and assumption of his current mechanical form. Whether this would actually hold in practice is debatable.
• None of these tainted worlds have ever been seen or encountered, but they have to exist somewhere in the Multiverse.