Immobilzed on the bottom of a pool

[Nichwee]

You've got an extremely powerful spell per RAW, then you seem to be ignoring RAW to make it an I-win button. Never mind the 'realism' of the monsters sitting drowning at the bottom of the pool

Firstly, he seems to have played RAW perfectly (saves were allowed, and the mobs were in LoE).

Secondly, he played the flavour nicely. The wizard had a focus for the effect and let it ride.

Lastly, the idea of sitting at the bottom of the pool brings to mind the end of Indiana Jones & The Last Crusade, where Indy almost dies trying to reach The Grail (despite having just tried to convince the "love interest" not to do so) and needed his Dad to shake him out of it - a granted save that he passed imo
The monsters kept trying to go for the loot convinced by the magic that just a few more seconds and they could get away safely, WITH THE LOOT.

 

[S'mon]

He did:
Emphasis mine.

ok, sorry.

 

[Uller]

You did at least give them a save to fall prone at the edge of the pool rather than enter hazardous terrain?

Edit: posted this before I read S'mons "ok, sorry" post so it is a bit more argumentative than it should be.../edit

Yes. 3 of the 4 were hit (so they were immobilized). One failed its save and went in, immobilized at the bottom of the pool. Round 2 the mage sustained it and hit all 3 outside the pool. All three failed their saves. I make al attack damage and save rolls publicly and remembered the +2 save for the one elite. The monsters were just rolling horribly. My expectation was for maybe one of the monsters to get stuck at the bottom...the rolls said otherwise...good for the PCs. It was a level 7 fight for level 5 pcs. Now they have the resources to press on and crush their foes in what looks to be a level 8 encounter. If the fight went as expected I think they would have cut their losses and went home having discovered the info they needed. Kudos to them.

So how am I not using the rules as written? Would I do this to the pcs? Absolutley. Opening adventure of the campaign was KotS...the fighter fell in the pit to be chewed on by rats and lit on fire by goblin fire bombs for three rounds. When on of the other pcs tried to help him out I had one of the goblins try to push him in with a bull rush. Admittedly I don't go for the TPK with creative tactics but I think it is important for PCs to be killed occasionally when they make tactical or operational mistakes.