I knew about the way you described, i just thought there would be a another comment which spawns shape 2 (or x) after x turns.
i.e. newmonster 2 2
spawn to monster #2 in 2 turns.
obviously there is no such command, my bad
Doing it with 25 forms is kind of boring, its a bad copy/paste job. Basicly, you could make 25 hydra units, and after every 5 you slightly up the stats.