In nature, the dominant animal need to defend itself. Natural is very brutal to fallen or weaken leaders. They will be kill and another raise to take their place if they are not strong enough to defend themselves from others.
Your fish is deformed, It is possible that he will not be able to defend himself or exert his dominant on the second fish. The second fish may growth and become dominant. When this happened, if the original fish is still a male then there will not be problem, but if he have change to female, then he will be kill.
You original, deformed fish need to be pair with a larger fish if he have not turn to female. If he is a she already, then she need to be keep alone for the rest of her life.
In my tank in the past (450 gal) I had a harem of Royal Gramma. The harem have been together for 6 + years when the dominate male get weaker, due to age I think. The largest female then turn male and promptly killed him and take over.
Right now I have a shoal of Lye Tail Anthias in my tank (320 gal) There are 6 Anthias originally. Reading that the ratio of Male to famales is about 1 to 8 in the wild. I added another anthias female to the tank. This is a small one. It seem that the male anthias spend a lot of energy patrol and exert dominant over the females. Anyway, the largest female, which is almost as big as the male, start to change to become male. The new male promptly kill the old male and take over. I am not sure why he was not able to exert dominant over his females. He may be old, or he may have too many female to harass over.
The point of my two observations above is that dominant fish need to be strong and exert their dominant over their subordinates. If they cannot, as your deformed fish likely will not able to, they will be kill by the former subordinate.
This is my thought you can take it or not it is up to you. Best of luck.
