This information is taken directly from the VS Battles Wikia site. So please give the members of the VS Battles wiki (especially the Admins) the credit they most definitely deserve.
Acausality is defined as the ability to exist outside of causality, or the natural flow of manipulation defined by cause and effect. An entity that is acausal has no true beginning or end, and is thus essentially immune to offensive causality manipulation and time travel.
Even if you go back in time and kill an acausal being in the past or prevent him/her/it from being born/created, it will still exist in the present and other timelines. Often, even if an acausal being is killed in the present, it can still survive by appearing from another timeline. Thus, acausal beings are very difficult to permanently destroy, often requiring the use of high-level reality warping.
Note: This power is based on causality immunity from Superpower Wiki.
- Depending on the user, they won't necessarily be able to emerge from different timelines if killed (or at least they won't be able to do so in a short time span, making this aspect of the power non-combat applicable). An example of this would be Sol Badguy, who could survive despite his past self being killed, but could otherwise die in battle and wouldn't come back.