You can only activate each effect of Zorc - The Dark One once per turn
The best way to counter a Delinquent Duo is to simply play a chaos deck, Thunder Dragon Chaos or otherwise
They involve going even harder on counter synergy
I personally run Spawnsire of UlamogSpawnsire of Ulamog in my Kruphix, God of HorizonsKruphix, God of Horizons deck, but only because I've run it by my group and they've all agreed that it's hilarious to dump a bunch of random Eldrazi onto the battlefield
An easy place to start is adding some of the other additional land drop effects, which were a little too pricey for me to go deep on: Azusa, Lost but Seeking, Kodama of the East Tree, Dryad of the Ilysian Grove, and Exploration are all excellent and will help you make the most of your explore triggers
Lol, I do have one or two Harpys Feather Dusters, can swap them out