A reader recently asked me to look at the hydra, but the hydra isn’t a particularly complicated monster. A straightforward brute, with extraordinary Strength and Constitution, it’s extremely stupid and not discriminating when it comes to target selection. It also has only one method of attack: one bite for each of its multiple heads, of which it initially has five.
Running a hydra encounter is primarily a matter of accounting: tracking how much damage has been done to it; whether any of that was fire damage; and how many heads it has at the moment, since (a) destroying one head without cauterizing it causes two to sprout back in its place, and (b) it gets an additional opportunity attack for every extra head.
The only question you have to answer, round by round, is where the hydra is going to position itself, and the answer is, wherever it can attack as many targets as possible, up to the number of heads it has. In other words, if possible, a five-headed hydra will try to position itself where it can reach five targets; a seven-headed hydra will go where it can attack as many as possible, up to seven; and so on. It doesn’t have to be immediately adjacent to these targets, since its heads have a reach of 10 feet: a target is still within reach if there’s a single square or hex between the target and the hydra, even if there’s another creature in that square or hex. (Because of the hydra’s size, an interposed Medium-size ally doesn’t give a humanoid creature any cover.) (more…)