"it's on my sheet" is not an explanation of an action
No, but it gives that character the ability to perform said action.
also, every rule has exceptions!
can something without feet be tripped?
Yes. And the argument for why this is the case has been repeated about a million times.
can something already laying on the ground be knocked prone?
Something that is already prone cannot be knocked superprone. But (and, as above, I predict that making this argument will have absolutely no effect) the prone condition is a mechanical effect that is part of an abstract set of combat rules and does not necessarily translate to anything literal. A creature that is already "lying" on the ground (as an ooze would) can still be knocked prone, imparting the appropriate penalties and requiring an action to right itself, unless that creature is specifically immune to the prone condition.
can something that moves 2 already, be slowed?
Yes. This is important, as a monster may have certain powers that only function on a slowed target.
Furthermore, a slowed creature's speed cannot be raised above 2, while a creature whose speed is already 2
can raise it above that value through powers or external effects.
It's a very common misconception that all bats echolocate. This is false. Only members of
Microchiroptera echolocate. Megabats (
Megachiroptera) navigate using more traditional senses, and
all bats rely on sight to a certain extent, depending on environmental conditions.
This is actually a pretty interesting challenge for you to bring up, since, presumably, in bringing it up you're implying that you would not allow bats to become blinded in your own games. Ostensibly, because bats echolocate and thus don't need eyes. Except that many bats
don't echolocate, so you could just as easily be creating an entirely
unrealistic situation by making your arbitrary ruling that ignores the abstract nature of D&D combat.
But, to answer your question in a more straightforward way, yes, bats can be blinded. Some of them have blindsight, and therefore are not especially inconvenienced by the effect.
can a stone golem be petrified?
Yes.