Kleptolisks are an ok monster for Vaults. Frustrating if you only brought elemental, steal things from you, etc. Puts you on edge just enough to not get bland. However, while charming, there's only so much to a Vault. Diversity could spice up the cashgrab if done right.

I'm suggesting three things for this thread: Puppy variants, optional mini-miniboss fights, and rare default-type Confetti drops.

First off, Crown Puppies. My idea is to, in a way, bring back the old, invincible "Gold Puppies", with a different skin set and a different method of "attack".
-Crown Puppies would come in three different reflective skins: Bronze, Silver, and Gold. All three variants are invincible, and can be only found in Treasure Vaults, with Tier 1 Vaults containing Bronze Crown Puppies, Tier 2 containing Silver Crown Puppies, and Tier 3 containing Gold Crown Puppies.
-All Treasure Vaults have a maximum of 2 and a minimum of 0 Crown Pups due to their charitable "attack" method:
-Crown Pups, when they detect a Knight, periodically shoot a Crown of varying type, the type of Crown shot being relative to the Pup type. Gold Pups shoot all types, Silver pups only shoot Crowns up to Silver in value, and Bronze pups shoot Bronze value crowns.
-Crown shot type is determined by probability; Gold (50cr) shots are the rarest from Gold Pups, and Silver-Gold (25cr) shots are the rarest from Silver Pups. Bronze isn't really affected much by this.
-On a per-Knight basis, Crown Puppies will shoot 20 Crown Shots, one at a time, directly at a knight within 3 tiles of it; the shots expire after 5 tiles. Shots made by the Puppy at other Knights while the Knight is outside of the 5-tile range will not be counted towards the 20-Crown shot limit for the Knight outside the 5-tile detection range, giving less incentive to be greedy and go for the Puppy while everyone else is farther behind.
-After 20 Crown coins have been shot at a specific Knight, the shots will no longer appear as Crowns (a sparkling mist based on crown color, maybe) and will not yield further payout.
-All Crown Puppy shots are infinitely piercing up until they cross the 5-tile dissipation range, allowing for the crown shot to affect multiple Knights within the radius.
-Crown shots are not affected by shielding, dashing, or shieldbashing.

Second, Confetti Puppies. Meant for purely aesthetic purposes, these Confetti-aura'd, reskinned Pups shoot a "confetti bullet" that trails default-colored confetti particles and explodes into a dense cluster of confetti (similar to the usable) when it hits a Knight.
-The shots deal no damage, and the Confetti Puppy exists on a spawn pad, so killing it drops nothing.
-The shots can be shielded against and dodged, but why would you want to do that? Celebrate! ;D
-The Love Puppy has a 1/3 chance to spawn over a Confetti Puppy, but it will drop nothing as it is a predetermined monster and exists on a respawn pad. Love Puppies spawned in this manner function normally.

Second, optional miniboss fights activated through means of a party button, or another group effort such as timed switches.
-The boss room would be near the elevator (behind it, perhaps?), clearly visible but also giving the clear impression that it wasn't necessary for level completion.
-The boss fought could be a beta monster such as an Ironwood Sentinel or even a Tortodrone for deeper Tiers/Stratums.
-Either that, or another miniboss, like a reskinned, more friendly-looking Battlepod that shoots firework rockets. An entirely new miniboss/reskinned miniboss for Treasure Vaults would be something celebration-oriented, as it ties in with the lighthearted Treasure theme.

Third, instead of the Crown trails leading to the main Treasure area, there is a 1/100 chance for a single predetermined Crown (not a drop) to convert to a default Confetti usable.

Feel free to provide constructive criticism and/or build off of ideas; I'd certainly like to hear what you guys think.