Let me do an analysis of what we see.
We begin seeing Eru riding Werewolf Sieger over Prisoner Beast. Since Prisoner Beast gives you a soulcharge when entering, at that point he minimum haves 3 cards in his soul.
We can see a second Prisoner Beast already on a rearguard, so it's 4.
Calls Gwynn the Ripper, 5.
Werewolf Sieger attacks, it's 7.
Next turn, he rides Master of Fifth Element, We are at 8.
Calls another Prisoner Beast, 9.
Activates Alluring Succubus's skill, 11.
Calls Gwynn, 12.
We are clearly missing 3 cards. In the parts we didn't saw he probably activated a Dimension Creeper (there is already a facedown card in the damage zone, so it probably happened) and called one more Prisoner Beast, that's the only way it makes sense.