Q: What tier is transcending space and time?
A: As said above, "transcending space and time" is a very vague statement by itself and can mean multiple things depending on the context in which it is made, as well as how this characteristic is portrayed in the first place. However, if it is specified that they "transcend space and time" in the sense that they exist on some higher level of reality that is
qualitatively superior to a spacetime continuum in nature, then they should be put at Low 1-C, assuming the continuum in question is one comprised of four dimensions. The answer may vary depending on this factor.
It is perfectly possible for a statement like transcending space and time to mean that a character is simply "untied" from the universe's spacetime, and is thus unaffected by alterations in the timeline and similar meddlings. It's not exactly uncommon for time travel (Or any action / process that affects something through different points in time) to be described as "transcending time and space." Transcend space and time can also refer to a spacetime continuum being different to a "regular" spacetime continuum (Say, a strange-looking reality that may hold a few different physical laws, for example) or slightly do be more complex than a regular universe, even significantly so, but not
qualitatively superior. Something A being said to "transcend" something B in real life can refer to the former being superior to the latter in some qualities in a notable way, but still roughly compatible. It does not necessarily mean transcendence not in an immeasurable way that would be graphically indescribable, such as A's qualities being superior to B by infinite amounts. With this in mind, statements of realities or beings with transcendence over space & time/the universe/etc., on their own, are not assumed to refer to
qualitatively superiority, unless of course further context may elaborate on and contextualize this.
It should also be noted that simply existing in some alternate state of existence that lacks time and/or space is not really grounds for any tier in particular, as lacking such things does not translate to being superior to them, and would most often overlap with abilities like
Acausality or
Nonexistent Physiology. A good example of a case like this is
Dormammu (Marvel Cinematic Universe), who is stated to exist in a realm "far beyond time," yet never actually displays any superiority over it, and is in fact vulnerable to time-based abilities due to his timeless nature.