Since the Monster World was the easiest to deal with between the two, Alister chose to deal with it first.
After Exoffus heard Alister's command, Exoffus led Alister to the end of the dimensional gap which if crossed, would create a dimensional gate from the dimensional gap to the other side which was the Monster World.
The dimensional gap and dimensional gates were essentially just the product of three world laws intersecting with each other. Rather than those three worlds merging to create an even bigger yet more chaotic world, the three worlds were connected by the dimensional gap and dimensional gates.
The World Wills of those three worlds couldn't interfere much since they didn't have a World Master behind them. However, the mastermind in the Technology World had a similar relationship to Fantasia's relationship with the World Will of the Magic Fantasy World.