Transform command is, I think, impossible. Rituals, iirc, will work on any unit(s) which is not what is desired. Though there is a transformation possibility here. I would say that chain of #firstshape would be better, or even making unresearchable #onebattlespell - unless somebody actually knows how The Eater of the Dead works!
We also could add to any of these possibilities some uncontrollability - for example, giving large dragons some Tartarian-style madness & making their final shape a neutral. This will make Dragons a viable alternative, but not a must-have.
A #onebattlespell alternative is cool, too. I'm not sure about it exact effects on gameplay, though. Testing may prove whether or not it makes conventional armies even weaker than SC prevalence does. But in any case I think this is a productive direction to look in. Also, does somebody know whether it's possible to take SCs out temporarily without banishing them to Cocytos?
