So after seeing Gobbler trainable, which was originally a TC, it gave me new ideas for spells that could be trainable through the Arcanum, whether they are all new spells, or just existed as a TC/item card before, or were exclusive to enemies only. Besides Myth, which already has Gobbler, here are some ideas of trainable Arcanum Spells. These are only trainable at level 100+ also.
Life: Leafstorm: does 265-305 to all enemies for 4 pips. 90% accuracy
Death: Death Ninja Pigs: 490 and -25 to next spell. 85% accuracy
Balance: Don't have an idea for a name or animation, but the effect would basically be a weaker spectral blast to all enemies for 4 pips. 85% accuracy
Storm: Storm Beetle: 125 and 25% to the next spell. 1 pip. 70% accuracy
Ice: Icezilla: 520-600. 5 pips. 80% accuracy
Fire: New spell: does 440-500. 4 pips. 75% accuracy.
These are just sample ideas, there could be more spells than this.