While i like challenging monsters, I think this one has too much built in player-screw.
- Turns a class ability into a class disability
- Can't stop the heads from regrowing at all
- Can't target the body to avoid regrowing heads
- Party gets punished for backing up the abused Tank [Rampage]
- Party gets punished for being lucky [hitting it with a crit recharges Rampage]
Weren't people complaining about how a foe could afford to easily just ignore the fighter's mark, take the penalty and attack someone squishier? Well, now, it has even more incentive to want to attack the tank over anyone else (an attack/damage bonus, on top of not suffering any penalties). What's not to like?
I like that it encourages parties to think out of the proverbial box. If you think that your party has become too effective/comfortable with a single tactic that they keep reusing, the hydra can be an answer to that. Now tanking is no longer as straightforward as the defender simply stepping forward and marking the hydra. They now have the weigh the benefits of marking vs the drawbacks against them.
I think this is the way solos should be. Tough enough to be able to stand toe to toe with the party on its own merit, without requiring any backup from other monsters. Many-headed ensures that the party will not be able to lock it down successfully with debuff spells, while hydra fury lets it spread the damage out more evenly (some bites will hit, others will miss, so you still take some damage, rather than none on a miss or a lot on a hit). This prevents its attacks every round from becoming too binary.
Interesting that this seems to be the 1st "anti-optimization" monster I have seen so far, where it possesses abilities that allow it to scale in difficulty relative to how powerful the party may be. If you can crit often, you still get the benefits, but the monster is suddenly more effective to compensate.
It still does not seem to do much to battleragers though (since they get temp hp per hit).
