Ravenous Bugblatter Beast of Traal
I went to disagree with you, cracked open my PHB to get a reference... and couldn't find what I was sure was there. So I took to the internet, and found "some ability checks take actions, some don't, there's no one-true-way" from a bunch of people, including in the SageAdvice twitter.@Blue the difference between web and this spell is web requires your action to escape. This does not. It just says, ‘if you want to move’ you must succeed the check. So you could still try to move and then do an action. If you caught in the centre of the whirlpool, you have to start making saving throws to escape or take damage. That part is more like web
So you're right, and I learned something. Thanks!