I have a creature with the Spell Tap trait: ‘This creature can’t cast spells manually, but can equip 3 extra Spell Gems. At the start of battle, your creatures gain copies of this creature’s non-Ethereal Spell Gems.’
I cannot select ‘Cast’ with this creature during battle, because the trait disallows it. This is fine.
However, if I set up the creature’s macro to instruct it to cast a spell, it will cast it no problem. If I am understanding the trait correctly, this should not happen.
The creature in question is a Nature Shapeshifter fused with an Ashmouth Cerberus. I haven’t tested it with any other creatures or Cerberus traits.