By now I’ve edited it in to my first post. I might compile it into a spreadsheet later, because a few Troops here and there are more difficult to research than others…
I would suggest the following internal guidelines:
- In general, a spell that combines a summon with other effects (e.g. Kobra, Spiritdancer) SHOULD NOT display “No Target Available” if the summon fails. Which is already the case with the majority of summoners (but not all).
- Inversely, if the only visible effect of a spell is to summon, the spell MUST display “No Target Available” if there’s no empty slot to summon into – e.g: Daemonomicon, Essencia (especially Essencia, whose spell does explicitly nothing without a Dragon Spirit alongside it).
- If the summon triggers at random, the spell MUST display “No Target Available” if the summon is attempted without an empty slot (e.g. Lyriath will display this message already, but Copycat does not)
Alternatively, you could create a different graphic (“Unable to Summon” or whatever) to avoid confusion with other effects that fail to trigger (like failing to deal Charm damage due to enemy team formation).