Secret Lair Drop Series (SLD)
The Secret Lair Drop Series has the set code SLD and the same symbol as PMEI. 

HTR also has the same symbol by the way I think this keyrune was duplicated.

Here are the examples from Scryfall:
HTR: https://scryfall.com/card/htr17/1/diabolical-salvation
SLD: https://scryfall.com/card/sld/5/snow-covered-forest
PMEI: https://scryfall.com/card/pmei/33/ja/lava-coil