Oozes: immune to physical damage. How to adjust CR?

[Skaven]

As the title really.

I was always bothered that you could stab or slash oozes and actually do damage / defeat them. It just makes no sense to me. Its ooze: it doesn't take damage, it just comes together the moment you pull back the sword. Its like attacking a pond.

However this presents a problem: if I throw in this house rule, how do I adjust the monsters CR? They are obviously a much more dangerous threat. The players will need to get creative if they have no magic energy weapons at lower levels, but similarly at higher levels of CR they will have access to sufficient blasting magic, so I cannot increase CR too much.

I just want oozes to be more dangerous, like in the blob movies. I recall fire and Electricity didn't seem to work well, they had to resort to using cold. So maybe halve damage from fire and electricity too?

[gkathellar]

The Swarm subtype already covers this, and like the Swarm subtype this will render melee ineffective against yet another type of enemy.

EDIT: Also, Jello doesn't magically fuse back together when you cut it with a knife. Just sayin'.

[supermonkeyjoe]

The way I see it is that oozes have an outer "wall" like a cell, the more it gets damaged the harder it is for the ooze to stay together.

[The Dark Fiddler]

The problem here is that you're thinking more of a very specific type of ooze rather than the creature type as a whole. Attacking most oozes won't be like attacking a pond because... well, they're not a liquid. In the same vein, fire and electricity may be very effective against some oozes, while cold could be nigh-useless. It again depends on the specific ooze.