In Arora world, there are many monsters who can't improve after reaching their racial limit.
For example, after reaching to D+ rank goblins can't increase their rank anymore. D+ rank is their racial limit.
Just like goblins, there are many monsters who are bound by racial limits and can't improve their rank after they reached to a certain rank.
Evan was thinking about turning rare monsters who are bound by racial limits into shadow undeads.
These rare monsters can be considered extremely powerful among the monsters of the same rank, but they can't reach a high rank because of their racial limit.
For example, there is a possibility that a goblin king may be born among the goblins. The Goblin king is also a goblin and it is also bound by racial limit.
But compared to normal goblins, a goblin king is far more powerful. Besides being more powerful than normal goblin, goblin kings are also very good at alchemy.