I remember exactly – 4 hydras joined... There, near the swamp castle. But you needed a stronger army... That is, you needed to have some monks or swordsmen... Basically, you just needed to build an optimal scheme for joining troops in terms of minimizing time... Through trial and error... But it took a long time to do even with cheats.
Well, you confused me, because you were talking about an island, and there were 10 hydras on the island...:)
And everyone had their own scheme in mind, but some people just came up with a better one. ;)