Monster affect clarifiction

[theyhavepeabrains]

If this question has already been answered please link me to the answer. If a person is in combat and someone uses Wandering Monster to add the Ghoulfiends card to the mix, does the effect of only being able to use your level to fight the Ghoulfiends affect the whole fight to where they can only battle both monsters with just their level? Same with the Insurance Salesman and only being able to use your bonuses? What if, hypothetically, someone were to add Ghoulfiends to fight with the Insurance Salesman or vice versa. They wouldn't be able to use anything right?