Ice Devil

D&D logic: cold is stronger against ice devils than fire. Go ahead, look it up.

Ice devils are only slightly below horned devils in the infernal hierarchy, with 14 RHD. Their ability scores are mostly inferior to horned devils, with the exception of intelligence and wisdom: perhaps the two least interesting scores to your average devil. They've got four natural attacks, but two of them you can't use with a weapon. To make up for this, their tail attacks have a chance of Slowing their target.

I know I'm sounding predictable here, but their other abilities are more of the same. Energy immunities, DR, regeneration, SR, telepathy... Almost everywhere, these abilities are slightly inferior to a horned devil's. A notable exception is their fear aura, which actually has twice the range of a horned devil's.

The SLA's are reasonable. Cone of Cold is solid blasting, even at this level, Fly you'd have to get somewhere any way, and Greater Teleport is still useful. Persistent Image, Unholy Aura and Wall of Ice should have uses. Only Ice Storm will probably never see use.

I'd be lying if I didn't have a LA in mind all this time. The Ice Devil seems to be a 'horned devil, but weaker' in nearly all aspects, and the ECL should reflect this. +2 for now, with an option on +3 (though I can't see that happening without the horned devil getting a higher LA as well).