I’m experimenting with Thylacine & Godspawn creatures. Spells cast by my Thylacine are not being cast by my Godspawns at all. Instead, Thylacine is casting these spells repeatedly, until the gem runs out of charges.
The team I tested this with is just Thylacine and Saurel. They were not fused and had no artifacts, so the only two traits were Eye of the Thylacine and Syndicate. I also had no relics or perks equipped. I tested this with a few different spells (Spectral Rain, Blood Spray, and Intimidate), same result on all three.
The attack component of Eye of the Thylacine seems to work fine. Godspawns are attacking enemies after my Thylacine does, as expected.