in fsc 5th vana phase he spawns more slags at the same time as something happens to cause a lag spike, making him spawn them twice at once so we get a bunch of hearts and then the two slags. that said, lag is still the toughest enemy in the game and needs a nurf, yet they instead buff it every update
More like a glitch than lag. Works mostly with stun, wich causes some monsters, including vana, to repeat last animation twice 8wich can backfire into a double attack)