How do ultimate spells work?

[Lickizard]

I understand to a certain degree ultimate spells cannot be cast automatically but they technically can under some circumstances (Feeling lucky will cast avatar spells but even AOE avatar spells will target random allies and enemies). So my questions is what exactly are ultimate spells?

Seeing as water salamanders trait failed to cast the avatar spell its probably not meant to be cast off of traits but can be cast off of spells is that a universal truth? Can no traits directly cast the avatar spell or maybe can random casting effects be the key to casting them outside of its own turn?

They seem to both count and not count as spell gems seeing as water salamander can't effect it so does that mean the white gemling trait wont copy it? If I used forbidden unity on another creature and have the ultimate spell as the only spell would that work? (under the assumption that its the only spell because they are cased to be at the bottom of the list)

[Lickizard]

They count as ethereal gems after testing I've done anything that says it effects ethereal gems can effect an ultimate spell.

Using the trait 'Roll The Dice' or the spell 'Improvised Recitation' definitely casts ultimate spell after testing but I don't know to what degree spells that cast or affect spell gems work on them all I can say it the water salamander trait doesn't work.

They seem to take priority to being on the bottom of the 'spell list' for something such as forbidden unity.