Stacking Black Tentacles and Web?

[GM Abraham]

Is there any point in stacking these two spells (i.e. casting them both on the same area)? Obviously, they offer two different ways of trying to grapple foes, one attacking CMD and the other attacking Ref, but what happens if they both succeed? Can someone be grappled twice, by two different sources? And is there any argument that the spells would interfere with each other (i.e. the Web get in the way of the Black Tentacles doing their thing)?

[GM Abraham]

Also, while I'm thinking about it, do Black Tentacles affect people who are flying? "This spell causes a field of rubbery black tentacles to appear, burrowing up from the floor and reaching for any creature in the area." Since they burrow up from the floor, I could see an argument for saying that they don't affect you if you are a certain height above, but what height? They create a 20' radius spread, so up to 20' high I guess...?

[Evilserran]

I believe, given the same rules for grappling, whichever spell grappled first would be the primary, the secondary spell would be considered "aiding" the first. So i would increase the escape dc by 2. This is a base extrapolation on the rules that exist, and not the letter of the law, but i feel more than reasonable.

You hit on the purpose of both, targeting different things, as well as needing two saves. Also web can be easily defeated with a torch, black tentacles cannot. As for the reach, i would conclude yes, they can reach approximately 20' up as well.

[Slyme]

Stacking tentacles with Grease is better ;)

Stacking it with Grease and Cloudkill is beast mode :P

[JiaYou]

Generally speaking, all spells that don't specify the height can be assumed to be a sphere/half sphere.

And about the grappling, I believe that is correct, that you can't be grappled twice. I would, however, like to see a scenario where two different monsters attempt to grapple and play tug of war with you.