On the Plane of Fire, run a rudimentary cellular automaton to make the lava slosh around, with a couple rules like “won’t encroach on radius 1 or 2 from the portal” and “there should be no net gain or loss of lava across the whole level”. It being static and the same every time except for the portal location is rather boring.

Make the Plane of Fire more interesting by:

• Getting rid of the fire traps (which mostly serve to provide lots of message spam).
• Making the entire plane constantly deal damage if you aren’t extrinsically immune to fire, more if you lack both extrinsic and intrinsic resistance. Being close to or over lava hurts you even more, and can deal damage even if you are immune or “like fire”, possibly based on how many of the 9 squares immediately are you are lava.
• Lava can erupt randomly from lava, which does major damage for levitating over it.
• Ensure the portal cannot spawn right next to the arrival location.

Lava on the Plane of Fire regularly erupts in a spray of molten rock, which is extremely harmful and thus very bad for you if you are over it or adjacent to it when it happens. This makes it less appealing to just levitate or fly and completely ignore it.

Every turn on the Plane of Fire, all scrolls and spellbooks in inventory or on the level are destroyed (except for naturally fireproof ones).