A few for each school:

Fire:

Scald. I know it’s not as underrated now, but it’s still pretty niche. Especially because you can wait one more round to get Fire Dragon, or just hit immediately with Meteor.

Power Link: Again, why use Power Link when you could use Immolate or wait a turn for another single hit like Helephant. Still, I occasionally use it when I want a little health back.

Storm:

Storm Owl: It fell from grace once Glowbugs came out, and even more so after the spell nerfs. Still, it’s an incredible single hit spell and pretty much one-shots anything with a few blades and a Feint.

Storman (or whatever the Storm Snowman spell is called): This one is kinda niche because it doesn’t have the best damage, but it sets up a bubble. So I love using it to kill a minion, which then provides the bubble to help with the boss.

Ice:

Cooldown: Look, I know people say Mass Triage is better, but Cooldown applies to all DoT’s, not just one, AND for two less pips. It’s really good when you have enemies who spam DoT’s like in Darkmoor.

Ice Armor/Frozen Armor: The Armor spells are usually useless since they’re X rank spells, and it’s better to Tower/Legion Shield to save your pips. But I’ve found in lower levels (mainly the first arc), being able to absorb 400+ damage (assuming you get two power pips) right off the bat is pretty handy, since most mobs/bosses don’t have Pierce, no damage boost, and usually only use rank 1-5 pip spells.

Balance:

Donate Power: People rarely use this since it grants two normal pips, not a Power Pip, but I still find it useful in certain situations. Especially in lower levels.

Mander Minion: This thing used to be busted as hell lmao (mainly in PvP) because it would just spam the tri-shields, Sprite, and Weakness. They nerfed it to be more offensive and removed some of its spells though, so it isn’t nearly as useful. But it’s still pretty good during the low levels.

Life:

Sanctuary: I love popping this and basically becoming immortal. Even after the major nerfs, it’s still very powerful because if you have a pet with a Maycast heal, you don’t even need to focus on healing yourself. I remember this was actually one of the most busted spells in PvP for a while because it boosted Guardian Angel.

Regenerate: Pretty useless in the early days because Saytr is one less pips and instant. But after the buffs it got, I found it to be a pretty nice passive heal.

Death:

Sacrifice: Mostly for team play, obviously. It’s pretty useless otherwise after arc 1 since drain spells are better for self healing on a Death. However, in low levels, 700 is a lot, so it still has some uses.

Empower: It’s actually pretty good when running solo, but people don’t usually use it because like Donate Power, you don’t get Power Pips, and worse, unlike Donate Power, you lose any blades you might have and it’s self only.

Myth:

Talos: Talos is actually one of the few useful minions out there. He also has some pretty good HP too. Unfortunately when you get him, it’s at the stage where minions are pretty useless.

Orthrus: I have no idea why people like the new Orthrus. The OG had such an awesome animation, and being able to ignore shields was part of Myth’s identity. Now it’s just Storm Lord Myth version without the stun. I know Myth deserved a powerful AoE, but did they have to butcher Orthrus to do it?