Chaos, also known as Random Tag, is one of the possible challenges (commonly called "handicaps" due to confusion with Challenge Mode) encountered in standard or challenge mode battles.
The Chaos challenge will cause your characters to tag in and out randomly with no control at all. This is particularly frustrating while fighting against Sinestro, all versions of which are empowered whenever his opponent tags out, as well as characters with damage over time effects or other debuffs (e.g. Killer Frost) that couldn't be immediately evaded by tagging out.
Aquaman/Prime's Atlantean Hero can be forcibly tagged out by Chaos, and therefore wasted.
- Chaos/Random Tag used to be a modifier for matches 5, 9 and 10 for Survivor, but was removed along with a large reduction to the opponents' stats, as it was extremely difficult and luck-based.