You need trolls that turn to stone in the sunlight, and goblins (or other fey) who have vulnerabilities to cold iron. Perhaps they can't cross a ward circle drawn in chalk or salt.
Come to think of it, you're right.
You need trolls that turn to stone in the sunlight, and goblins (or other fey) who have vulnerabilities to cold iron. Perhaps they can't cross a ward circle drawn in chalk or salt.
Perhaps the two worlds shift around relative to each other? That is to say, maybe-- from the goblins' perspective-- a particular portal (or whatever connects the two worlds) opens near Lumberbrook Village tonight, but opens onto the Desert of Howling Wastes tomorrow, and onto the courtyard of Goblinslayer Keep, then an empty glen, then the Sea of Acid Tears, then an owlbear's lair, then another village, and so on over subsequent nights. This may or may not be predictable with astrology or divinations.EDIT: I think what I am trying to convey is I'm looking for a reason that goblins wouldn't be trying a Trojan Horse strategy of laying in wait until dark. Looking for a reason they have trouble establishing a foothold and claiming territory in the real world.
Something else I'm tryin to model is that goblins can stay in our world past the break of dawn, but really don't want to. The vulnerability to sunlight is a great start, but I'd like some other reason why they want to make their raids and then get back to an area that will vanish back into their realm rather than just hide somewhere in ours until sundown. Maybe that doesn't require a mechanic. Maybe it's just the same for the as human adventurers. Why camp in the enemy's turf and risk discovery if you can make it back to a safe place? Ultimately PCs would probably have a few adventures like that - go raid that goblin fort that appears in the canyon every new moon, but get out before dawn or you'll be stuck in the shadow realm.
EDIT: I think what I am trying to convey is I'm looking for a reason that goblins wouldn't be trying a Trojan Horse strategy of laying in wait until dark. Looking for a reason they have trouble establishing a foothold and claiming territory in the real world.