Shapechange.
Turn into something Large, tough, flying, and with Regeneration, and you're pretty much set.

Gate or Greater Planar Binding:
Call a Pit Fiend. It flies, has Fireball as an at-will spell-like ability, and it regenerates. Have it zap away from a thousand feet up. Should do the job, sooner or later.

Elemental Swarm:
Eh, not really the best, but it can get the job done.