The event system could be implemented as follows with tools partially present in the game:
- An announcement comes on the screen.
- Players (of all server types) are invited to join the server where the monsters are attacking.
- Special NPCs appear at the entrances of the city and offer the players to join a special platoon to defend the city before the invasion.
- At the given moment a red circle appears around the city which indicates how far the monsters must be repelled.
- PVP mode is momentarily disabled.
- The NPCs in the city disappear (easier) or panic.
- Soldiers in the city gather where the monsters will attack (random monster spawns in several points around the city).
- The event starts on a given time (ex: 30mn or more)
- Monsters attack.
- The event ends when the monsters are kept in a grey area beyond a red circle until the end of the period.
Rewards :
- Monsters give normal Elvia zone loots (depending on type and city attacked)
If the challenge is won by the players, they receive a gold bonus from the dedicated NPCs.
The more efficient the player was, the bigger the bonus (AP cap possible for more challenge)

Translated with Deepl (free version); thanks to it.

I agree, BDO needs server-wide pve events that isn't just a boss. An event like this will make the game feel like an MMO.

Lag also shouldn't be a concern. It can be instanced at an entry point and distribute players evenly, or it could be similar to RBF with joinable lobbies. 

I actually really like this idea. Depending if its elvia or serendia elvia, adjust ap varying from the similar ap/dp requirements. One major town weekend raid would be also really nice, like calpheon/heidel, and keep the smaller cities raids like Glish or Treant regular, throughout the week. For me it would sure break a monotony of grind for cup cookies when ocasionally needed.

I think that's the potential drawback. People coming to leech the even just like they are world bosses. So equalizing the gear would be bad.
But rewarding players for being actively involved in the event is good. So yeah. Drop a zerg, from imps to orcs in Glish throughout the week and similar in Keplan. But let players bring their own guns to the fight. AP cap'em just like in the normal grind zones and maybe tier rewards based on total damage dealt/taken/healed.

Great idea! Having npcs just run their mouths about the dangers with no dangers ever happening is... immersion-breaking :P

Glad to read your comments, wasn't sure that the idea get some success.

Good reward on success would be individual to prevent leeching. Global reward for successful counter strike could also exist, but caped on XXX mobs killed. If the player juste seat and see, he just get nothing.

If the players loose the counter strike, no reward at all. It give a good motive to win.

Elvia world have the advantage to be already empty. Populate cities with Soldier NPC on event could be done, animation and partly action "AI" is already there , because they are the way to locate the invasion. Normal NPC is more délicate. Creating panic animation is fresh new work, running away animation could be take on pre-existing.

Red circle arround the cities could be take from Battle Arena.

Many players are reluctant to go in Elvia's world, because they thought they aren't strong enought. The event could be also a way to make a more pleasant discovery and getting Elvia's loots. No being alone fighting strong monsters is conforting.

(sorry for my english, not really the best)