'Summon' type mobs near 20.
 

Where's a good spot with mobs to use the anti-summoned line against? I'm thinking Lavstorm rock dervishes, but where else?

Imps and Elementals in Najena and Sol A. Any pet casters (najena mages, CT SK's, etc.) will go down pretty quick once you roll through their pet.

Still out of your range I'd imagine, but the Hole is excellent for these spells too as I recall.

Near 20, I think that's the best. Elementals, wherever you find them.

Might be a bit too high for them but there's earth elementals in Steamfont.