Abel realized that he was facing Duriel possessed the world stone fragment. The only way to deal with it was to open his own world stone fragment ability as well. Since he wasn't using it, even the fastest "lightning" spell could not hit his target.
With that in mind, he locked onto Duriel and activated his world stone fragment's acute vision and digitalization ability. Duriel's movements started to appear slower when he did so. As he regained his confidence to carry on, he took out a hell creature's corpse from the personal storage box and resummoned more skeletons. They were meant to block Duriel's attacks. Two was the maximum number of hits they could take. It wasn't quite enough, but it was enough for him to make a rough calculation of how Duriel moved when it attacked.