A gigantic skeleton suddenly sprouting from the ground to fight against the Primordial Beast Nidhogg is not something that was planned. Still, the plan to contain and kill the Primordial Beast Nidhogg has already been scattered through the wind because of the power shown by the enemy. Creepysoo is currently controlling the gigantic skeleton undead at the sacrifice of not using his own undead knights.
All the additional health and strength of the gigantic skeleton is due to the fact that his undead knights' own souls were used as catalysts. This would not mean that his undead knights will no longer be revived but they cannot be revived while the gigantic skeleton is active. Also, if the gigantic skeleton dies, Creepysoo's undead knights will also be unable to be summoned for quite a while.
