AkshatArpit
Arnold is honestly the perfect mage for dealing with a swamp because he can use Ice and Earth to build stable and safe roads. Of course, for the ice, he needs to be able to make the ice thick enough to defend against any attacks from anything in the water, I dont think he is fully capable of doing that now. In the case of Earth, he would need to reinforce the Earth to be sturdy enough to defend from massive monsters and super powerful humanoids destroying it which is probably even more difficult than creating a floor of Ice over water. He can just lead an army through the swamps and have his summons clean up anything that the army cant deal with. But they have to be completely thorough in their extermination or else the path they build behind them could be destroyed as they most past that area. Plus then you have to logistics going through that area which would require a decently sized security force, depending on the amount of resources being moved. It can be done it will just take a while probably a few months. Maybe a year if the enemy actually has a properly trained army which is probably what is going to happen.