Hydras made their 4e debut in the first Monster Manual, and here we get a few more of them. Their basic lore remains the same and you can check it out on the original post I made on the subject.
The hydras on this entry have several passive traits in common: Threatening Reach allows them to make opportunity attacks out to their full melee reach, instead of only against adjacent enemies. Many-Headed makes it resistant to being dazed on stunning. These conditions only disable one of its heads for a turn. And Regenerating Heads causes the hydra to lose a head at 75%, 50%, and 25%, regrowing two others at the start of its next turn.
The number of heads an hyda has is important because of Hydra Fury, an at-will power that allows them to make a bite attack for each active head they have. The effect of an individual bite, and the starting number of heads, vary per hydra.
Mechanically, MM2 hydras are kind halfway between the ones we saw on the first Monster Manual, and the ones from the Monster Vault. Most of their mechanics still work like in the MM1, but Regenerating Heads debuts here and reappears in a slightly weaker form in the Monster Vault. With the MV version you can prevent head regrowth by dealing fire or acid damage to the hydra before the start of its next turn, but nothing can stop it in this version.
These hydras are also lacking the Darkvision and Swim Speed of their relatives from the other two books, though they still have trained Perception and All-Around Vision that prevents them from being flanked.
This species of hydra is covered in gleaming metal scales and has extra-sharp serrated teeth. It’s drawn to the scent of blood in much the same way a shark is, and one head bites a victim the others get into a frenzy. Because of this, it’s also known as the Blood Hydra. They are Large Natural Beasts, and Level 16 Solo Brutes with 640 HP and a ground speed of 7. They start with four heads, gaining extras at 480, 320, and 160.
A razor hydra’s bite has Reach 2 and inflicts stackable ongoing physical damage. A healthy target would take ongoing 5 damage (save ends), but if the target was already taking ongoing physical1 damage, then that damage would increase by 5 instead.
A poor sod on the receiving end of a razor hydra’s Fury attack would have ongoing 20 damage (save ends) to deal with, assuming all four bites hit. A single save will clear it all, but if that save fails and the hydra bites again, the total will increase even further. There’s no cap!
The Blood Frenzy trait makes it so the hydra gains a +2 bonus to attack targets who are bloodied, or who are taking ongoing physical damage. That’s one more incentive for it to focus fire on a single PC.
Once the hydra drops to 0 HP, its Ferocity allows it to make one last Hydra Fury attack. At this point it will have seven heads, for a potential 7d8+28 damage plus 35 ongoing damage against a single PC.
This interestingly-named hydra occupies the same narrative niche as the one Hercules faced in his labors. As a Huge Natural Beast and a Level 20 Solo Brute, it’s likely the most powerful hydra in the natural world, and is stronger than any PC who isn’t an actual demi-god or equivalent. There are stronger specimens, but you have to travel to the Elemental Chaos to find them.
Heroslayer hydras have 776 HP and five heads at the start of the fight, gaining new ones at 582, 388, and 194. Its bites are Reach 3 and have no riders, though its Hydra Fury deals 10 extra damage to any target hit by two or more bites. Rampage allows it to bite every target in reach and inflict 10 ongoing damage to every target it hits. It recharges whenever the hydra suffers a critical hit.
The titular Heroslayer trait is a big “Fuck You” to defenders everywhere: while the hydra is marked, it gains a +2 bonus to attack and a +5 bonus to damage against the creature that marked it. Yes, this applies to every individual bite in a Fury combo.
So here we have a hydra with a decent incentive to spread its bites around until a defender marks it, when it will instead focus exclusively on the defender until they’re good and dead.
This is one of those stronger species native to the Elemental Chaos. Chaos Hydras start out with only two heads, but their bites are very strong and infused with deadly elemental energies. The new heads it grows when wounded also gain new random elemental abilities.
The Chaos Hydra is a Huge Elemental Beast and a Level 22 Solo Brute with 848 HP. It has two Reach 3 basic bite attacks, one for each head: Frostfire Bite deals fire and cold damage, and Storm Bite deals lightning and thunder damage.
Whenever the hydra grows a new head (at 636, 424, and 212 HP), it gains a new bite attack chosen by a d4 roll. It can gain multiple copies of the same attack. Its Hydra Fury allows it to bite with the two original attacks and any new ones it might have gained.
The four additional bites deal less base damage but have “save ends” riders. They are: Crushing Maw, which slows and deals ongoing 10 damage; Mind bite, which dazes; Paralyzing Fang, which immobilizes and inflicts a -2 penalty to all defenses; and Venom Tooth, which inflicts ongoing 10 poison damage.
Thematically this hydra is all over the place, but that’s the point. It’s hard for PCs to protect themselves from everything it can do.
Sample Encounters and Final Impressions
Hydras are solitary, so you will usually only find one of them at a time. However, they’re also frequently followed by opportunistic scavengers who feed on the remains of their meals and who might be impatient enough to give them a bit of help with killing those meals. Examples given are carrion crawlers and shardstorm vortex elementals.
Occasionally, a powerful character might be able to capture a hydra for use as a guardian. The example encounter given is for this scenario, with a razor hydra and its minotaur cabalist master.
Hydras are cool, particularly those with the regenerating heads mechanic. However, I think they should be used sparingly to prevent the novelty from wearing off.
I say “physical”, but the strictly correct term would be “untyped”. Untyped damage is almost always dealt by physical attacks, but you could have magic powers that also did it. It’s written like “1d8+5 damage” or “ongoing 5 damage” instead of “1d8+5 fire damage” or “ongoing 5 fire damage”. Very few monsters resist it, but none are particularly vulnerable to it. ↩