Will it Blend?

We just did the achievement successfully. Took some tries to work it out.
What we did:

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• Everyone bought one of each of 4 items off the vendors at the start of the dungeon, as linked above by Belazriel ([item=187178], [item=187179], [item=187173], [item=187171]) - they are unique when bought, so you can only buy one of each.
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• You need to throw the items in front of the boss when he does "Interrogation". At this point, a player is put in a cage and needs to be freed from the cage while the boss walks toward him with a flurry of blades. These blades destroy the melon, tentacle, plushie and glow sticks.
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• The remains of the 4 items splatter through the room - puddles will spawn near all players. Everyone needs to stand IN the puddles to get debuffed. The debuff seems to stay for the remainder of the fight.
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• Every player needs all 4 debuffs from the 4 items.
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• We started at the first "Interrogation" by throwing in a fixed order: one player put melon, another the tentacle, and so forth. We put these directly in front of the boss and then proceeded to free the interrogated player from his cage. By then, lots of colorful puddles spawned near us / on us and since we stood close to each other, most of us got all debuffs at the same time. :)
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• On further Interrogations, we tried to fill up missing debuffs, since our caged player from the first interrogation could not move and did not get hit by all puddles. We did this rather chaotically, but after the second or third interrogation, everyone had all 4 debuffs.
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• This is when you bloodlust / heroism and kill the boss.
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• We suspect this is a personal achievement, so it should be possible to kill the boss and have at least some players get the achievement, and later reset the dungeon (if needed, with help of an alt and a fresh ID).
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• The achievement even pops when a player dies to the boss AFTER having all 4 debuffs: our hunter died and made us kill the boss anyway, so that at least the other 4 of us would get the achievement. To our amazement, even our hunter got the achievement, while being dead on the ground (and had no debuffs in his dead state). Thus, it seems to be OK to have all 4 debuffs at some point in the fight and then kill the boss, even when casualties happen.
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I hope this helps someone to get this done a bit quicker than we did. :)

Did this last night with another guildie, based on trial of the other comments it took us about 6-7 tries before we got it.

Items Needed
*These are unique, so you can only buy one of each.*

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• [item=187178] from Toy Vendor for 100g.
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• [item=187179] from Antique Vendor for 100g.
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• [item=187173] from Meat Vendor for 100g.
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• [item=187171] from Fruit Vendor for 100g.
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Vendors are located at the entrance of the dungeon.
Note: There are only so many of each item available for purchase, not sure whether the items respawn after a certain amount of time. So there may only be a limited amount of attempts available but cannot confirm since we did not end up needing more than about 4-5 of each item.

Strategy that worked for us, with current patch:
You can indeed do this with two players, however, we believe one of those two must be a hunter or another class with some sort of tanking pet or ability where it can tank the boss away from the group. It seems tanks and healers will not get targeted with Interrogation. Doing this with only two players, there is no room for error. If someone misses their throw or the boss doesn't hit the item, you have to restart over. Having more players will increase the room for error due to having more chances (duplicates) to throw the items.

Based on our trials, I would say this is near impossible to do it with the same player getting targeted all the time. This is due to the way the mechanic works for this achievement. Once the boss hits the item that was thrown, the puddles are a splash effect, only lasting about 1 second. The player who is stuck in the Containment Cell doesn't have enough time (or very little time) to get out and run to a puddle before they disappear. You would have to have some very, very good RNG to have a puddle spawn directly under the player imprisoned.

The boss prioritizes ranged dps players, so have everyone who has a ranged spec, switch to that to maximize the amount of people who can be targeted (at least 2). We figured this out because the boss was always targeting me (hunter) and not my guildie (priest). Once he switched to Shadow he started to get targeted.

Currently being level 70, shouldn't really need too many heals but a healer is helpful since they can still heal some in off spec. The way we did it, you do take some damage from being in the Containment Cell or hit in the face by blades.

It doesn't matter on the distance you stand from the boss, getting targeted with Interrogation is random.

The Interrogation fails about 70-80% of the time so DO NOT throw your item down until you see it successfully cast, you'll know this because there will be a laser beam from the boss to the imprisoned player and the boss will start to walk slowly towards the player with his blades rotating in front of him. When you see the laser beam, throw the item in-between boss and imprisoned player so the boss hits it. Important - Give yourself enough time to throw and make the landing, Don't aim right for the bosses feet, throw it roughly in the middle in-between boss and player. Throwing it too late or close to the boss will fail as the boss may not hit it and walk right over.

The items have a 1 minute CD upon throwing one and are only up for 1 min. So just take it slow and only throw one item at a time (unless you're running with more than 2 players).

Do not break out the player out of the Containment Cell until after you've gotten the debuff, doing so before the boss has time to shred the item will end the Interrogation.

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Summary
Have at least two players, one being a class that has a tanking pet. If only two players, both should have ranged dps spec otherwise this will not work. Everyone buys the four items needed. Start the fight and have the pet tank the boss from across the room so there is more distance between players and boss when Interrogation happens. Everyone should be standing in a group together. Wait for Interrogation to actually cast (laser beam from boss -> player) then throw down one of the items (or more if 3+ players) for boss to shred (aim for middle of the beam or closer to the player stuck in Containment Cell), giving enough time to cast and land the throw. Boss shreds item and sends out the puddles. Everyone not imprisoned then gets in a puddle and gets the debuff for that item. After the debuff is received, break out the player imprisoned. Keep doing this until all players have all four of the debuffs, then kill boss and you win! Remember to heal your pets, as they do need healing over time.

Achievement was fixed in patch 11.2
Party of full 80 - works as intended.