Runes and rune machines

Runes are bits of magical 'code' that does a very specific action, such as "Fire a magic missile" or "activate when a creature comes within ten feet". Runes are created by battle mages, and allow them to stay relevant at higher levels of play, due to the more intricate spell effects they can use.

No rune an duplicate a spell above fifth rank, and runes are difficult to create due to battlemages not having a formal magic education.

A rune requires a fatigue charge to function, but it can hold a charge indefinitely until activated.

Rune Machines: Runes can be assembled in any combination so long as the total number of unique runes is 3^n, so one rune, three runes, and 81 runes are all valid, but six runes is invalid (unless if three of the runes are duplicates, so aaaabc is valid, but aaabcd is not, but abcdefghi is valid.)

Rune traps generally have a trigger and two effects, due to the higher fatigue investment required by larger rune machines.