The goblin army didn't spawn when I used goblin battle standard item. It consumed the item, but no goblins spawned. I haven't collected enough tattered cloth to try again yet.
It is indeed possible to summon the Goblin Army using the battle stand, although there are a few notes that should be taken:
A Goblin Army (and all later invasions) spawn around the center of the map, with the exception of the first wave, which will come from east or west. This will be announced through the message : "A Goblin army is approaching from the east/west!".
After the first wave reaches the center of the map, all future waves will spawn around the center of the map.
The amount of Goblins that will spawn is 80+40 for each player in the world.
You cannot summon a Goblin Invasion if:
- You have less than 200 health.
- You haven't smashed any Shadow Orbs/Crimson hearts yet.
- If there is another invasion going on.