TEXTURES:
*SLIME1 or *SLIME2 or *LAVA1 or *LAVA2
ENTITIES:
misc_fireball (for lava)
WHAT TO DO:
Make a water brush as outlined in the previous entry. Texture the whole brush with one of the recommended textures. That's it. 
OPTIONS:
If you want to use normal WATER textures but want the damaging effect, copy the water brush. Designate the copy as a trigger_hurt entity. You can even alter the damage rating of this entity for greater flexibility. If you want fireballs to pop in and out of the lava, make a brush and designate it as a misc_fireball entity. Place it inside the lava brush. Adjusting the speed of the fireball - this is hard to judge since the fireball's height randomly varies, and may require a bit of trial and error. You don't want the fireballs to literally shoot through the ceiling.
Crucified zombies: make a brush and designate it a monster_zombie entity. Enable the crucified flag for this entity. Move the bounding box of the entity 12 units into the wall to make it look right. 