Below is a list of ideas and suggestions that came to my mind while playing PvP.

1) Sneaking into keeps
I don't know if this is already implemented, but if an enemy player is not in combat, perhaps they should be able to sneak into a keep? Say a zerg was sneaking to the door, they could get inside without a need for sieging. Of course, this would not work for the front door, because guards would be in charge of opening them (lorewise). The postern doors, however, are just doors. Get your sneaky boots on cats! We're sneaking inside!

2) Lockpicking postern doors
Being able to unlock a postern door with a lockpick would be nice. Perhaps a player must pick the lock to get inside? Counter-measure: you can lock your doors at keeps. Time to scout your keeps, because enemies could be sneaking inside! Or maybe they might already be inside...?

3) Disguise
If the game were to have disguises, they must be implemented in a way that a whole zerg would not be able to use a disguise (that would be too obvious anyway)... This is tricky to think of how a disguise would work, but one thing is for sure that enemy players would not recognize them as normal guards, but with enough attention, they can.

4) Running with an elder scroll
They are taking our scroll! Quick, protect it!
~~ How about somebody take it and run? I think that allied players should be able to pick up a scroll and transport it someplace else, or run until the enemies are cleared. When an ally picks up an elder scroll, the pickup would not be announced to the campaign (for secrecy), but when they drop it, it will be announced. When a scroll is placed in another keep, or placed back where it belongs, it is announced to the campaign.

5) Counter for thieves
Now it seems that with these features, zergs will no longer be a bunch of soldiers, but rather a band of thieves. I have no idea how to counter this at the moment, but hopefully we can come back to here soon.

6) Counter for Thieves Guild
Do we really want EVERY soldier in an army to be a member of the Thieves Guild? Surely, there must be something in the game preventing players from becoming thieves. Maybe a jail system might be implemented? That when caught stealing, guards would confront the player? Like a normal TES game. Bounty on your head.

7) Guild faction: Guard
Ever wanted to be a guard? You cannot become a guard if you are a member of the Thieves Guild, and vice versa. With this faction, you can arrest players! Currently PvP is a slaughter arena. Only one person wins. If a jail system really is implemented (keep dungeons?), perhaps that is where enemy players who are captive can go... until rescued. This is a neat way to diminish enemy numbers. If a player is arrested, they can only be brought to a keep dungeon if they are within a certain area of the keep. Press E to have them transported. If they are captured on the field, then you are going to have to make-do by leaving them there (siege box with bars for building a cell right there? Maybe I am asking for too much). Perhaps on your bounty missions you might be able to arrest your enemies instead of killing them?

A guard player can arrest another with bounty (a thief), but must check them first. if you find a player to be suspicious, check them. If they are guilty, you can arrest them, and possibly fight each other in a PvE area... or maybe just arrest them. Arresting players in PvE zones would send them to the nearest town jail/dungeon. It would be awkwardly traitorous to arrest allied thieves in Cyrodiil.

Being able to capture players certainly might not be a great thing to do; jailing players against their will. maybe there could be a way to break out of being tied up when arrested? Use main attack or a gameplay feature like lockpicking? Or when you are jailed, maybe you could forge a lockpick and pick the lock to break out? Good luck getting past the npc guards. Rebellion!

If you log out inside a jail cell, you will still be there.

8) Counter for Vampires and Werewolves
Just like a bunch of thieves, we don't want the battlefield to be filled with bats and wolves. Maybe a third world skill line could be implemented so players would WANT to be pure hearts. Maybe this has something to do with the Divines, or maybe Race skill line would be nullified, or a skill line just plainly for normal people. Anything so endgame goals would be to avoid vampires and werewolves.

But then again, werewolves and vampires can still be nice people, so take back that Divine part.

9) NPCs and Alliance Points
If this is not already a feature being developed, it would be nice to be able to buff the NPCs at a keep. 15k to bring guards to higher veteran levels at resources, and 25k for keeps. Maybe more things than buffs would come in the future?

10) Experience and Alliance Points
Here is my version of getting experience:
+12,000 exp/ap for successfully retrieving an elder scroll from an enemy keep.
+1000 exp, +100 ap for defeating a VR10, must be alive and landed a hit within 10 seconds.
+900 exp, +100 ap for defeating one of top 10 players of enemy alliance that is currently online (by alliance ranking, and not the whole alliance, due to inactive players), must be alive and landed a hit within 10 seconds.
+700 exp, +100 ap when capturing a flag.
+700 exp, +100 ap each time the warlord send in equipment.
+20 exp, +5 ap when more than 1 player is healed when healing.
+20 exp, +5 ap for every kill in PvP, +40 exp, +10 ap if landed a hit on enemy within 10 seconds.

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How are the ideas?
Comments!