It’s a layered impact point.
The whole blast looks like this:
Layers< TransitionEffectL<TrConcat<
// Impact Flash
TrInstant,GreenYellow,TrDelay<25>>,EFFECT_BLAST>,
// Waves
BlastL<White,850,250,351>,
// Impact point afterimage
AlphaL<TransitionEffectL<TrConcat<TrFade<300>,Rgb<255,70,70>,TrFade<300>>,EFFECT_BLAST>,BlastF<700,250,100000>>,
// Impact point
BlastL<White,300,350,100000>>
>