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ENZ0 switched in Heatran (lvl 100 Heatran ).
Pointed stones dug into Heatran.
Heatran lost 12% of its health.
Gengar used Pain Split.
Gengar restored 50% of its health.
Heatran lost 40% of its health. Gengar lost 10% of its health.
Since Pain Split does direct damage, I guess it counts as an attack, which triggers LO recoil. To confirm this, I guess it's worth checking to see if Taunt blocks Pain Split.
But IIRC, Taunt blocks Pain Split, which complicates things.