Which spells do folks consider worth learning or upgrading ?

[PHJF]

Fire Rain (infinitely better than fireball)

Ice Snake (for fire resistant enemies like dragons)

Poison Skull (again, for fire-resistant ememies; also potentially does more damage than Fire Arrow)

Pole Axe (really only if you haven't found Ice Snake yet)

Lightning is a massive waste of mana, so ignore it. Damage is actually lower than Ice Snake, yet it costs 15 more mana (and that's WITH archmage's staff).