I think there multiple summonings maybe accepted. But not necceserily so. If hero has about 12 different summons, it can fill all battlefield with creatures:-) So maybe first summon (if made by hero not by artefact or starting spell) will make other creatures non accessible.
There must be
“val”:5 //5 hit points for each 1 spell power summoned
There is also WOG artefact summoning random dragons at start of the battle. I think it also can be implemented some way through this spells type.
There also an idea of Demonology skill (like in HMM4) increasing effectiveness of summoning spells, so this must be throught out in complex…
PS It will be good if spell to fix (resurrect) NON_LIVING creatures will also be realized.