The Vault of Stars dungeon is unlocked by completing Uncovering the Threat in the Sharandar Campaign. When queued in hardcore mode, 3 additional mini-bosses are available. After unlocking the dungeon, one key for the second chest can be purchased daily from the campaign store.
Loot[]
Campaign tokens[]
[A Dash of Hope], 
[Golden Apples], 
[Ashen Star Dust], 
[Crystalline Leaves] are used to purchase gear from the campaign store. Each boss drops 0-2 tokens to be rolled by the group. Only 1 token can be obtained per boss per week.
Vanity pets[]
[Malthar], 
[Prince of Frost] and 
[Gloaming Court Golem] are dropped by the respective bosses. 
[Lumi the Spirit] drops from the Mounds and, possibly, bosses. These are personal drops, not visible to the teammates.
Crafting ingredients[]
[Shard of Dawn's Light], 
[Shattered Snowflakes] and 
[Displacer Beast's Whisker] are crafting ingredients dropped by the bosses (personal drop). 
[Corpse Flower Thorn] drops from the Corpse Flowers (group roll).
Artifact set[]
Bound-on-equip 
[Sparkling Fey Emblem], 
[Starshard Choker] and 
[Twinkle of the Stars] have a chance to drop from the bosses (personal) and from the end chests.
Rings[]
Rings from the Accessories collection of Sharandar can be obtained from the end chests.
Hardcore armor[]
Each mini-boss has a chance to drop 0-2 pieces of armor from the Antiquities of Sharandar collection (personal drop, requires pick up). The 2nd mini-boss has a small chance to drop 1525 IL pants (group drop, requires pick up, not in the collections). The 3rd mini-boss has a small chance to drop 1525 IL shirts.
Hardcore rings[]
[Band of Air] or [Ring of Darkness] can be obtained from the special vines after collecting 4 ingredients and finishing the dungeon in hardcore mode. 
[Petrified Root Band], 
[Shambling Mound Moss] and 
[Thorn Covered Sepal] have a ~5% chance to drop from respective mini-bosses. 
[Night Diamond Shard] has a ~30% chance to drop from the final boss in hardcore mode.
Ingredients are personal drops and go straight into the inventory, without the need to pick them up. The ingredients are character-bound and only one copy of each can be carried at the same time.
The rings are account-bound and multiple copies of each ring can be obtained by the same character. However, that might require unequipping the ring or even putting it away into the shared bank or mail.
Guide[]
Shambling Mounds[]
A few Shambling Mounds are encountered throughout the dungeon. One of their attacks is a red AoE around the mound. This attack puts a deadly DoT on everyone it hits. While it is possible to cleanse the DoT or heal through it, the AoE has to be avoided at all cost.
1st mini-boss[]
The first mini-boss is located behind the waterfall, on the left, before the first boss. It is commonly farmed for the gear even by players who have not completed the normal version of the dungeon.
1st boss[]
Shortly after the start, the Royal Gardener spawns 4 Corpse Flowers, puts red circles on 4 players, spawns zombies around the flowers and disappears.
The red circles should be put at the edge of the arena. The resulting pink ground does significant damage and applies slow debuff. The debuff can be removed by blocking.
The key to the success in this fight is for the tank to aggro and kite all of the zombies, while the damage dealers quickly kill them before the boss returns.
Some of the zombies will have orange glow, link to one of the players, slow him down and explode upon reaching their target. The explosion increases the Soil counter and makes the fight more difficult. These zombies cannot be controlled, although the slow debuff can be removed while blocking. Kill them as soon as possible.
While away, the Gardener uses two powers. He targets one of the flowers with the green line. The line should be interrupted, preferably by a tank or healer, while the damage dealers clear the zombies. If not interrupted, one of the flowers becomes red and active and eventually increases the Soil counter.
The Gardener also targets one of the players with a red stripe. The player should put a flower between himself and the Gardener to destroy said flower.
After returning, the Gardener uses single-target Sever the Stalk ("tankbuster") attack, which has to be taken by the tank.
At 50% HP the group has to fight a displacer beast. The beast puts a DoT on a random player, does a frontal AoE attack and summons a weak clone. There are 3 key mechanics during this phase, picked randomly.
The Gardener shows up at the edge, the beast starts to stare at one of the players (who does not have the aggro). Shortly after, the beast pins down the target and a black line from the Gardener to the target appears. The target takes damage over time from Maul: 5 ticks over 5 seconds, ~90k each tick. The black line has to be interrupted by the tank and does large AoE damage.
The group should stay away from the edge of the arena to leave some space between the Gardener and the target, while the tank has to spot the Gardener and the beast's target to interrupt the line in time.
Another mechanic is Fungi explosion under the feet of each player. It has a red circle and must be avoided.
The third mechanic are the red circles from phase 1. Place them at the edge of the arena.
Once the beast is defeated, the Gardener returns. In addition to the phase 1 mechanics, there will be a Shambling Mound moving towards one of the flowers. If it reaches the flower, the mound heals to 100% and starts attacking.
2nd mini-boss[]
The portal to the second mini-boss is located to the right of the campfire before the 2nd boss. Tank should go forward and will be met by a swarm of Quicklings. Do not panic, control and kill quicklings before they attack. More quicklings will spawn during the fight. Avoid the AoE around the mound at all cost.
2nd boss[]
The boss has 4 key powers: frontal cone AoE, "hypothermia", Ice Statue and Ice Patches.
Stay behind the boss for the frontal cone AoE. The AoE is significantly wider than the red area shows in mod 22 and the hit is deadly to all except the tank.
Stay together, behind the boss, for "hypothermia" (multiple arrows pointing to the same target, red zone outside of the small safe circle around it).
When a single player gets a single arrow with a red circle, he should move away from the group, usually to the centre. After the player gets iced, he should be quickly broken out of it.
When everyone gets a red circle under their feet (no arrows), stay together on the boss until the ice forms under your feet, then move away (usually clockwise).
The Maze[]
If you get separated from the group, wait for the rescue.
In the arenas, the same mobs always spawn at the same spots. The tank should aggro Elven Warriors and the rest of the group should stay and move together, on the edge of the arena.
Active companions (as opposed to augments) can help to avoid some of the initial attacks. Keep moving if you get aggro.
3rd mini-boss[]
The third mini-boss can be found after the 2nd arena in the Maze. That place with a barrier can be found in the normal mode as well. The normal mobs in that room can be carefully avoided, but the mini-boss itself is surrounded by a swarm of quicklings.
3rd boss[]
The 1st golem should be pulled into the light to remove his reflective shield. After 50% he will announce the change and has to be kept on the edge of the Void Pool to be stripped of the shield.
Do not attack the golem while he is shielded and you see blue numbers. That damage still generates aggro. The reflected damage is capped at 50k and is further mitigated.
3 Void Pools are stationary and one is moving. The tank should stay outside of the pool to avoid getting the speed debuff, while keeping the boss on the edge of a stationary pool. The debuff can be cleared by stepping into the circle of light. The Void Pools remove the shield from the boss even while overlapped by the circle of light. After some time the Void Pool is used up and the boss has to be moved to another one.
Stay behind the boss for the frontal cone AoE. The AoE is significantly wider than the red area shows in mod 22 and the hit is deadly to all except the tank.
Stay together, behind the boss (except the tank), to share the damage from "hypothermia" (multiple arrows pointing to the same target).
The 2nd golem transitions between phases at 66% and 33%. He also does a frontal wave attack shortly after "hypothermia", move behind the golem.
The 3rd golem transitions between phases at 75%, 50% and 25%. He also summons Blackholes (not to be confused with Void Pools) that pull players in and do damage.
The tank has to keep the golem facing directly away from the Blackhole, while the rest of the group takes hypothermia and blackhole damage inside the Blackhole (without the tank). This is done to prevent the frontal AoE attacks from covering the Blackhole and the group pulled into it. It is a heal check.
The tank can wait for the first Blackhole and cone AoE before luring the 3rd golem into the light.
If the tank gets targeted by the hypothermia, he should move through the Blackhole so that the Blackhole is very close, behind the boss. That way the group can stay in the Blackhole, share the hypothermia damage with the tank and still avoid the following frontal AoE.