What are the pros and cons of running crobat and galarian weezing on mono poison? When would crobat be better than g-weezing and vice versa?
I'll do a comparison of sorts for you so it's easier to see.
Galar weezing: More physical bulk which allows it generally easier use to be able to switch in and check threats (as long as you pay attention to the HP), fairy typing (important vs stuff like garchomp, roaring moon, useful in the dragon matchup as you can see, while the fairy typing and ability means in a vacuum it has better resistances and whatnot overall). Access to useful tools such as will o wisp.
However, pain split is not reliable recovery, it holding black sludge means it gets chipped by the rocks it's supposed to defog and is shaky (I emphasise this cause you can win vs these, but it's risky if you don't know the interactions) vs kyurem, hydreigon and gmolt (despite being designed to help in those mus, we'll get into this later). Other interactions like mold breaker excadrill means you have to be extremely careful.
Crobat: actual immunity unlike levitate to help play around pokemon such mold breaker excadrill (assuming choice lock of course), reliable recovery in roost (unlike pain split galar weezing holds), higher speed tier and brave bird to check mons such as non-scarfed cinderace, greninja, meowscarda, alakazam, torn t in a pinch, but most importantly, mega gallade (something galar weezing can barely do at best), infiltrator with toxic (important because you get to deter sub roost kyurem, sub plot hydreigon and the potential sub plot g molt from breaking down your team), can hold boots to ignore stealth rock and thus reliably defog them without getting chipped on switchin (which is what you want for a defogger)
However, does not have the sheer bulk or unique and great typing that galar weezing has. Can be hard to switch in sometimes as a result and takes a bit better positioning.
As you can see from this, they both cover different mus and whatnot despite both functioning as the ground immunity for the team. They are both good for poison. It just depends on what you want to cover and play to.
