Based on Ashlands, I assume that the Deep North mobs can use your portals and will just show up and destroy your base and gear even while you're wearing it. Naturally, there will be six hundred of them at once, all of them will have homing ranged attacks that do 4800 base damage, and the final boss will literally delete your save with an unavoidable one-shot - and there will still be players who insist it's brilliant game design.
