acid pit and large animal companion

[Titania, the Summer Queen]

So lets say an enemy fails it save and falls into an acid pit. Your large animal companion climbs into it after the enemy. The animal fills up the space directly above the enemy, the enemy needs to remove the animal companion before it cano escape the acid right?

[Barry Armstrong]

There's other ways he can escape the acid, but, yes, the basic mechanics would be that the animal companion occupies the block above the enemy, and he has to bypass it somehow to escape.

[Relixander]

Typically, a medium sized creature does not actually occupy the entire 5' cube of space. This is also true (perhaps more so) when creatures get larger, a large creature does not usually completely occupy 10' cube of space, the additional space is provided for other game mechanics.
Typical ways to go through enemy square include (but may not be limited to), acrobatic movement, bullrush, overrun, the fact that climbing is involved may change what is available to certain creatures.

[Titania, the Summer Queen]

I would make the DC to get past the large creature the same as it would me to jump over it. At least if the acrobatics skill was used. Since you can't overrun (charge) while climbing, I would rule that out.

Unless they have an actual climb speed of course.
For acrobatics( jump) I guess a DC of 60 would be sufficient .15 feet to make it into square above the large creature.