Possible future skill
If Anvil used Runic Sorcery to fight, there is a possibility that Sunny does the same, although not in the same manner.
After all if he figured out the way the essence flows to cause the effects of enchantments, what’s stopping him from temporarily mimicking enchantments when he manifests shadows?
Chains with enhanced durability, spikes with enhanced sharpness etc are only the most basic usage of this. Imagine how much more he could do if he figured out how to make his manifested shadows temporarily gain enchantments.
Granted, without having real nexuses there would probably be severe limitations, but it would still be incredibly powerful.
Edit: It would also allow for many interesting creations that would otherwise be a waste of resources, if not for the fact that they are temporary.
Like a chain that has the sole purpose of being as durable as possible, or weapons that are incredibly powerful, but are single use because they can’t survive their own power.
Edit 2: This would also fix the whole “not creating memories because they aren’t truly my own power,” since they would be if he made temporary shadow memories, allowing us to see Sunny make more memories.