In Chapter 1122 we see the Iron Giant releases a massive Haki attack which sends the Elders (minus Saturn) back to Mary Geoise, allowing the Thousand Sunny to land safely on the sea. A flashback occurs to when Joy Boy tells Emet to use that Haki he implanted him with when the time is right.

It does seem like Conqueror’s Haki is the key to defeating the Elders in their monster forms. Which makes sense honestly. I think the Five Elders were given their powers by Imu, whatever that power is, and is probably a big reason why they appear to be immune to any permanent damage. Though they can still feel the pain. I think it’s fair to say that there is a chance that the Haki that the Elders possess are possibly borrowed from Imu. And I still think the Elders are Devil fruit users, since that Haki burst canceled their transformations.

From Imu’s reaction there, it definitely feels like there is a direct connection between Imu and the Elders, almost as if it was Imu projecting his power through them via the summoning/teleportation ritual thing. Imu felt Joy Boy’s Haki as much as everyone else at Egghead did. Imu is definitely physically/emotionally connected with the Elders. That’s the main reason he felt it. The Haki did not reach Mary Geoise by itself, it stayed around the island.