A: As the
Tiering System specifies,
destroying or creating multiple timelines or space-time continuums is usually ranked between 2-C and 2-A, depending on the number of timelines involved.
However, there are two edge cases, which require particular considerations.
First, note that in our terms a universe, and hence also space-time continuums and timelines, always includes all of the three dimensional space that can be reached from it. That is to say, any place that can theoretically be reached via regular three-dimensional movement alone (e.g. via spaceflight) would be considered as part of the same universe, and hence timeline, regardless of whether the fiction considers it as such. Traveling from one universe to another should only by possible via portals, higher-dimensional movement, teleportation or other unusual means of transportation.
By default, universes are assumed to have separate three-dimensional spaces, but should a piece of fiction demonstrate the opposite destruction of several timelines connected in such a way would only be Low 2-C (Universe level+).
Second, is the case of timelines that at certain points are connected. Contrary to the case where one can always travel from one universe to the other via three-dimensional movement, it is only possible in those at certain times. In fact, at certain points in time they might be the same universe. E.g. if a timeline branches into two, then the timelines were the same universe before the branch split happened. And for the other way around, if two timelines get merged into one, then they are the same universe only after they were fused.
In those cases, the destruction of any one timeline is only counted if it was not connected to any other timeline for an infinite amount of time. Otherwise, if there are several timelines none of which are separate for an infinite amount of time, they would all be counted as just one timeline for the purpose of tiering their destruction or creation.
Note that timelines, by default, are assumed to be infinitely long i.e. it’s assumed that there is no end to time. Hence, unless the contrary are shown, the destruction of timelines that branch out from each other, and then never merge together again, would still be ranked between 2-C and 2-A (depending on the amount).
The underlying idea behind all of that is that each timeline that is counted should still be a large four dimensional object, as that’s the fundamental criteria to qualify for those tiers.