Hitting a hydra

This is a mechanic for determining which head of a hydra gets hit. I swear this is simpler than it looks. If the logic doesn't immediately make sense from the chart, read on rather than scratching your head over it.

Heads	Dice rolled
1	-
2	-
3	2d2-1
4	1d2+1d3-1
5	2d3-1
6	1d3+1d4-1
7	2d4-1
8	1d4+1d5-1
9	2d5-1

In some games (e.g. DCC) you are already tracking the HP of each head of a hydra. In some (e.g. 5e) you are not, instead tracking only a, HP total and the number of heads. If you're already keeping track, this isn't a ton of extra overhead.

If a player chooses to strike at the hydra without aiming, roll the listed dice to determine which head is hit. The dice are simply a pair of dice whose maximums add up to the number of heads, plus one. For instance, 9 heads, plus 1 is 10, half of that is 5 so you roll two d5s. The reason you need to subtract 1 is because you can't roll a 1 on two dice, so you end up with as many possibilities as heads.

If there is only 1 head to hit there's obviously no need to roll, and if there's only 2 then just let the player hit whichever one they want. I considered a 3-in-4 roll to hit the desired head but it's getting too complex at that point.

Optional extension: Aiming

If the player aims for a specific head, treat that head as the "center" roll: the most likely roll on the pair of dice (the smaller die total plus one (yes, with different die sizes there will be two equal results, that won't matter)). Lower numbers go down the line, higher numbers go up the line, and the ends wrap around (aiming for the first head and rolling low can hit the last head).

This lets players be strategic if certain heads have certain abilities, rather than the center ones probably dying first. It also allows for players to try to kill the heads all at the same time.

Alternate version

Roll the two dice together. The leftmost die represents left, the rightmost die represents right. Literally just use where they land on the table relative to you. The difference between the two dice determines how many heads the player misses by, and which one is highest determines the direction.

This version came from a hexcrawl "lost" mechanic where two dice determined how far left or right travelers drifted.