The 8th stage of the annual John Van Caneghem Tournament (2007).

I remember clearly - 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 too long to do, even with cheats.