Q: What happens if I fall into lava?Are there rules for lava? Am I just missing it? It's in a lot of descriptions, but what's the damage, and does it restrict movement (per Magma critters)?
Lava Effects. It's also in the Dungeon Master's Guide.
If you have access to the DMG II, you'll want to check out the Lava part on pg. 53 in the Archtypical Locations section.
Of course, Fire & Brimstone is good also.
Those are 3.5 rules, just FYI. This is a 4e rules forum.
The first poster is correct.
"Your feet have just burned off. You fall prone."Instant death is the main idea. The only save is to see if you can drop prone before going in. Reflavor the prone in any way you would like.