FlipBizcut,
You wrote:
"Hmm...maybe remake it completely and on death it is replaced by two or three Children of the Hydra...could work."
How about this. Instead of having the Hydra grow new heads for every X kills it makes, it starts with one head and, just to throw out a number, 600 hitpoints.
When it loses 200 hitpoints (now down to 400), the first head "dies" and is replaced by 2 new heads, it's hitpoints go up 100 (now back up to 500), and it's attack doubles.
This process would keep repeating until it's hitpoints finally reach 0 (for this to work the Hydra either can't be healed OR it can be healed, but only up to the new, lower hitpoint max).
For balance purposes, the numbers would have to be played around with to find the right combination so it's tough but not impossible to kill. But the idea would be consistent with the original concept of the Hydra from the 12 Labors of Hercules; every time a head is chopped off, 2 grow to replace it, constantly regenerating itself. Thus it was a true labor because it took forever to kill the darn thing.
Here's one possible sequence for accomplishing this concept:
1) Starts with 600 hitpoints, 1 head
2) Head 1 "killed" when hitpoints reach 400
3) 100 hitpoints added (now 500), 2 new heads grow, attack is double
4) Another head is "killed" (leaving 1 head) when hitpoints reach 300
5) 100 hitpoints added (now 400), 2 new heads grow (total of 3), attack is tripled
6) Another head is "killed" (leaving 2 heads) when hitpoints reach 200
7) 100 hitpoints added (now 300), 2 new heads grow (total of 4), attack is quadrupled
8) Another head is "killed" (leaving 3 heads) when hitpoints reach 100
9) 100 hitpoints added (now 200), 2 new heads grow (total of 5), attack is quintupled
10) Final 200 hitpoints of damage kills the Hydra completely.
In the end, this adds up to 1000 hitpoints of damage needed to finally kill it; I think that's not too unbalanced given the current Hydra starts with 800 hitpoints and can be healed (whereas the Hydra I'm proposing can't be healed OR can't be healed beyond the new, lower hitpoint max).
Opinions?