Does nothing if the calling actor has no valid lastenemy field.
If that lastenemy is in its Death state or a subsequent frame, the calling actor explodes as if it had collided with something. Otherwise, its horizontal velocities are adjusted to match the lastenemy's. This use of the lastenemy field means this codepointer can only work as intended if it is called by actors created through A_LightningZap.
This codepointer is restricted to LightningZap and derived classes.