space = ascend
currently i have duck/crouch bound to "c" but i doesnot work for a descent while in vanish mode

To be fair, does it even work when you are *not* vanished but are noclipping? The way you wrote it suggests it does. But, the answer to my question should be "no" as it is a game-thing and not a Vanish-plugin-thing.

There simply is no keybind to descend. Would be nice if Facepunch added one for noclipping-use, though, or indeed make it so it uses the crouch keybind to do it. As it stands, currently the only way is to look down and press your forward key to descend again.

cause crouch is the descend key for drone and heli, if im not wrong. Yep i didnt get why it doesnt work while nocliping, probably code limitation.

If ure modding a server, i suggest u use a pluging called Telekinesis from WhiteThunder.