Lightning
Thurisaz (ᚦ), the yellow rune. Thor is built on it. Chain Lightning arcs through every Lightning block on your grid, and Storm-Caller splashes his Lightning matches across the whole enemy line, then calls a bolt down on a deep chain to turn another rune Lightning. Lightning Focus and Thunderhead lean the build harder still.
In detail
Block 5. Base spawn weight 1.0, with Thor's affinity adding 0.5 and Lightning Focus another 0.15. Storm-Caller fires on every chain step reaching depth 2 or deeper, so one cascade can strike several times. Lightning Rod adds 2 damage per stack, takes a stack for each Lightning match you clear, and keeps them for the rest of the run; the value listed on that charm is its tick interval, not its damage.
More in glossary
From the current development build. Content and balance may change before release. This public reference includes discoveries and does not reflect your personal unlocks.