Speed infinite – I would say it is space-Time Manipulation from the
Spatial Manipulation page. There is precedent in the series from
Glenda’s
case which Rimuru’s feat seems to be better.
I am fairly sure Immeasurable or infinite speed would be too inconsistent; some threads discussing
past inconsistencies on speeds; though some points might outdated from current speed rating because of more evidence.
Infinite Prison is weird; it looks too small to have High 3-A range.
It is stored in Rimuru’s stomach, which has limited space since
finite things can fill percentage of its capacity, so this point basically nullifies the infinite size.
It seems bigger on the inside going by the
percentage filled from it compared to the part of a lake that Rimuru swallowed in this stomach; Infinite Prison is implied to be even bigger, but it could largely be based on Rimuru’s stomach, which is weird like a
metaphysical (chapter 31.5) space or pocket world where
things (chapter 17.5) can be
created (chapter 17.5) out of imagination (could be from subjective reality) and strength, which is basically irrelevant to it.
Unless there is more solid evidence, I saw Infinite Prison as basically a strong forcefield with spatial power created out of infinite imagery space.