Finding Jarvia will take The Warden's party through the entirety of her tunnels. The carta uses many traps in their defenses, so a rogue is highly useful in order to disable all detected traps.
Jarvia is surrounded not only by her faithful carta members, but also in the centre of the room (where she stands and will regularly move herself to) by explosive traps on each side. While these are not generally fatal to a member unless they have very low health, they'll knock affected characters to the ground, making it far easier for Jarvia to attack.
The best strategy is to take care of her lackeys first and then tackle Jarvia herself, or have a tank working exclusively on Jarvia while everyone else deals with the rest of the carta members.
Having your party wait near the entrance and casting Storm of the Century on the center of the room can allow to deal heavy damage to Jarvia and her lackeys whilst keeping the party out of range.
Once the battle is over, weapons and loot can be stolen from Jarvia including a key. If the Warden is working with Bhelen, don't forget to plant the incriminating evidence against Harrowmont. Harrowmont on the other hand just wants her and her carta eliminated.
On higher difficulties, especially Nightmare, be careful of the traps in the center of Jarvia's room. Not only can they knock party members down, but they also deal monumentally more damage than in lower difficulty settings. Weaker party members can be one-hit by them, and tanks will still take a heavy hit from the explosion.
Fisty's Strategy (You need: a mage with Forcefield, and a Warrior with taunt): Run your tank into the middle of the room when the fight starts, then Taunt, wait to see if you've drawn nearly everyone's aggro (if you haven't you're doing it wrong), then use Forcefield on your tank and start tearing away at everyone attacking your tank. Rinse and repeat. *Tested on Hard*
Tip for Jarvia encounter: This tip applies ONLY provided you have Shale in your party and he has Rock Barrage learned. At the very start of the battle, select Rock Barrage and apply it so it covers pretty much whole room - trigger it, and in pause mode, make sure that once it is triggered, all members are out of the spell effect area. This will weaken the first wave of minions to the point where you should be able to kill them quickly (which will get your warrior if he has Death Blow learned easy stamina for more powers to use). Then try to focus on Jarvia with your party. Make sure Shale stays alive to use Rock Barrage again (Stoneheart is very useful to regain enough stamina). Trigger Rock Barrage again, get your party out of the way, this should kill off or significantly weaken the second wave of minions. Then just focus on Jarvia and kill her. 3. If you need a bit of shelter from those lot of bows while waiting for Shale's Rock Barrage cooldown, or just can't focus on all those minions while Jarvia is still around, you can position your party members behind columns on each side close to the stairs - this should lure some minions, but mostly Jarvia to you.
Tip no.2: 1. Make sure you have enough health poultices and lyrium potions, having smaller amount of those can make this battle a pain. 2. Shale's Rock Barrage makes this battle easier as it can be a basis for the tactics here, it deals a lot of damage and stuns enemies, so you can focus on Jarvia who is a strong opponent by herself.
- "You caused a lot of trouble today. Beraht lost a hundred sovereigns for Lord Vollney."
- "Kill them! But leave the mouthy one alive; I have plans for him."
- "Kill them! But leave the pretty one alive, I have plans for her."
- "So Bhelen realised his throne means nothing if he can't hold onto it, yet he still doesn't bother to send his own men?" (If the Warden supports Bhelen)
- "So Harrowmont finally realised we're taking over the city, yet he still doesn't bother to send his own men?" (If the Warden supports Harrowmont)
- "Well, you picked the wrong side, stranger. It doesn't matter who's king, as long as there's a queen!"
- Jarvia has a unique weapon, "Jarvia's Shank" available to players who purchased the Rogue pack for Dragon age 2.