The guide to Sky Pirate Drake

Since noone seems to have posted one yet, and a lot of people in my faction have been asking how this Primal World random quest works, a guide!

Finding Sky Pirate:
Sky Pirate Drake will appear above unstable areas within the Primal World, or so it is written on the Daily Event (Mirrorflower). I guess the whole of the Primal World is unstable, since he literally can appear anywhere above the Primal World (main world, not the story mode).
A red server notice will inform every player when he has spawned. When this notice comes, you can go search for him in the Primal World. Sky Pirate likes to fly a little higher then most flying mobs - he is typically found around a height of 40 to 50. When a player is near, he will banter a bit in the normal chat window - look for this to know when he is near. Sky Pirate looks like one of the Skyrage Shark Earthguard fliers (or the Airship Guide NPCs between Inkstone Village and Luneska) - but is a bit larger.
Search thoroughly. He can be literally anywhere. I've found him directly above Kirin Town (rather amusing as a party just popped out of FSP - instant bonus event), but also at the very northwestern corner by the Miststone Ruins. The location appears to be randomly chosen.

Fighting Sky Pirate:
Fighting him is easy. He will not fight back. Simply wittle his health down with whatever your highest DPS methods are. As with any "?" type mob, pets do high damage - venos, storms and mystics can use their summons to do a lot of damage fast.
Peckked mentioned that the boss will start it's escape while at 50% health, and that the boss should NOT be killed completely, or the portal will not appear!

Entering the Mirrorflower Treasury:
Once Sky Pirate's health is low, he will escape, leaving behind a portal. In order to get into the treasury, fly into the portal. You don't need to have done ANY damage to sky pirate to use the portal. Simply fly into it. The portal remains for only a few seconds after Sky Pirate is gone, then it vanishes too. Ranged characters might not get sucked into the portal when Sky Pirate despawns rightaway, if that happens, simply fly into the portal manually. You'll automatically be teleported into the Treasury.
Asterelle mentioned that in order for the portal to work, it has to aggro you (similar to the teleporting NPCs in the UCH entrance). Peckked mentioned that you should not have summons out, as the portal will try to aggro them and might fail to port players as a result.

The Treasury:
The treasury is divided up into a number of similar areas, and you randomly get dumped into one. The areas seem identical - i guess this was done to allow multiple players to take full advantage of the treasury. So invite your friends when Sky Pirate is found! Have a squad signet ready!
The Treasury has various mineable items:
- Mini Coral: Digging this gives you Ginseng Tonic Rice Balls, which is basically untradable Herb Yunxiao (5000mp mana potions). I'm unsure about the actual amount per mini coral at this time.
- Large Coral: This gives you "Coral". You can use the item for 10 Feastworthy Crab Dumplings (3500hp potion, untradeable Crab Meat basically).
- Giant Conch: Digging this gives you a Conch. You can use these to gain 200 Vitae.
- Giant Pearl: Digging this gives you a Pearl, and the Giant Pearl will not disappear. But! You need a Pearl Picker, which you get by killing the 2 small NPCs which roam each area.

There is a time limit to the treasury - after a short time (exact amount unknown at this time) you will automatically be ejected from the treasury back into Kirin Town - of course all your loot will still be with you.

Merchant Sokka:
You can use many of the items directly, but for a stronger effect, trade them with Merchant Sokka. You can find him in Kirin Town left of the Untamed structure (376 460). Sokka's trades work much like divine emissary quests and he will have the purple icon for them. In order for them to show, you must have at least one Coral in your inventory.
Common trades are:
2 Pearls for 10 Primordial Bloods
3 Conches for 1000 Vitae
10x Coral for 100 Crab Dumplings + 100 Ginseng Tonic Rice Balls
Rare (purple trades) include:
1x Pearl + 10x Coral for 1 War Avatar Pack A
1x Pearl + 1x Conch for 2 War Avatar Pack A

Trades cycle daily, so if you want packs, keep checking back each day. You can take a trade quest even if you don't have the items yet - it'll stay in your Divine Emissary quest listings until you find the items required.

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I'll update the guide if people have more information, feel free to post your own tips!
12 April: Guide updated!