With the node slime series, the shadow and wicked node slime masks, I'm pretty sure there's one of each currently reported. In general the special themed node slime stuff is fairly rare

Dangerous Dragon Wings are also fairly rare.

Most promo gear that aren't direct reskins are fairly rare, especially the celestial ones.

Definitely going to be an accessory. Honestly with all the prize boxes in existence I wouldn't be surprised if there are lots of really rare items.

Remember the Gemstone auras? Barely anyone played when they released so I don't think there are a lot of them (especially the last few Gemstone auras). I might be wrong though.

Oh boy hopefully not a lot of people remember what I put last time but decided to 'meh' and returned LONG ago already and actually got interested in this topic. Hmm the rarest of the rare eh? Welp I'll list some in my experience the ones that I hardly see as well as ones most people if maybe not all remember or have overlooked. Will start with auras then the rest; with costumes there's a lot so might not list as much with these.

• Twinkle Aura - barely see anyone with this one anymore or probably since it's barely noticeable I/we may overlook it; personally have one.

• Unclean Aura - not as rare and been seen but not a lot of people have it.

• Aggro Aura - only seen a few with these but before one of the flash sales where it popped out it was incredibly rare and had a very small chance chance (believe it was <0.5%) to get; personally have one.

• Blossom Aura - only a few people have it but due to the trailing creating lag, some may have them but never take them out.

• Dreadful Aura - only like 3-4 exist I believe and know the people that have it. Rarely taken out if there's more because of lag possibly.

• Soaked Aura - one of the overlooked auras with the first to have a splash audio to it. Seen one or two on AH but never seen on a person besides like 2 to 3 people.

• Rose Aura - another rare aura with at least a few people having it but possibly more if not for the lag it creates.

• Gem Auras - how it was mentioned above, some are more common but others are less likely to be seen. Varies depending on whoever that has them is on at the time.

• Snipe Aura - wasn't hear for that promo but only seen a handful of people had them.

• Leaf Auras - particularly Wicked and Marsh, rarely seen a lot.

The more recent auras I don't count because imo they need some more time until they can be considered rare and people start talking about their possible rarity depending on how many are unboxed or bought. Now for the other accessories and won't list them based on body section:

• Prismatic Barrel Belly - Only seen one person have it, not sure if there are more. Divine and shadow may fit this category but divine may be a little more common.

• Prismatic Bomb Bandolier - Seen two people with it, no one else with it. Hunter may apply but listing the ones that you get from iron lockboxes and the monthly ones you get in the prize wheel after finishing a level.

• Prismatic Canteen - Only one or two people have I seen it with, not sure about the rest.

• Prismatic Com Unit - Seen one person with it, not sure about the rest. If I'm listing more prismatic at this point it is because these types of accessories tend to have lower drop rates than the rest. Divine and shadow may fit this category as well.

• Divine/Prismatic Game Face - Never seen anyone with these, heck I'm sure not a lot of people have game faces. Possible that some do but I haven't seen them yet.

• Prismatic/Volcanic Glasses - Haven't seen these two in a bit. Seen divine on auction house with a buyout but the prismatic ones I have seen two on the featured section. Possibly more are around. At this point you may consider 'oh but what about the promo ones because some items from those are rarely seen too'. While this is true I'm only listing the ones that some people overlook because with the promos there are some events where you can get the boxes from past promos, such as the Anniversary ones therefore you increase your odds in getting them. Plus a ton of boxes have been opened in the past so it's possible that these items are around ¯\_(ツ)_/¯.

• Arcane/Polar/Bloom Halo - Blossom is a little more rare than the other two but they aren't excluded since only a few people that I see have them. Polar became more uncommon however and was known to produce a puffy effect at times. Arcane is rare as well with only a couple laying around; I have one Arcane.

• Prismatic Maid Headband/Regular Headband/Maedate/Wide Vee - Seen only one person with this.

• Prismatic Long Feather - Not sure about this one so I'll add it in there.

• Divine/Prismatic Helm-Mounted Display - Barely see anyone with this unless some know people who have them.

• Prismatic Ribbon - Seen two people with it, possibly more out there.

• Shadow Toupee - I've been told this was rare and since I have one and a couple of people have told me what kind of toupee I have due to the dark color. Seen three people with it.

• Prismatic/Divine/Volcanic Scarf - The first is the talk of being one of the extremely rare items since only 3 or 4 are known to exist, possibly more since I seen a few out there on some people I know. The other two haven't seen much but have a friend with the divine one.

• Prismatic/Divine Side Blade - Don't see a lot of people with these two.

• Prismatic Vented Visor - Don't see this one often.

• Prismatic Vitakit - Becoming a little more common since I seen a few people sell them but mentioning it.

• G1 Wings - For this one the prismatic ones are excluded since they are more common than the others. The regular ones may vary but have rarely seen anymore.

• Wolver Tails - The prismatic one is excluded but some of the regular ones are more rare than others. Imo Toasty is the most rare one but it depends on how many times others seen the rest of the tails.

• Prismatic Parrying Blade - This one a few have but is rarely seen and it kind of amazes me that they're not that high in demand, plus I heard they sell for very low too ¯\_(ツ)_/¯. Personally have two.

• Divine Dragon Wings - Heard that these are barely seen anymore but are being a bit more common since a few have been on the featured section in Auction House. Still rarely seen and seen two people with them.

• Wings of Rage - No not the Wings of Fury those are the yellow ones, these are the red ones. I heard only ONE person has them and no one else, but I did see them on said person.

• Polar Wolver Tail - Pretty rare but seen on two people. Still rare however and seen one selling around at times.

• Prismatic Ruinous Crystal - Been seen on flash sales a couple of times but surprises me that almost no one has them on or seen a lot. Possibly being held to be sold for high price.

• Power Pistons - don't see these anymore but were a bit common back in the day.

• Shadow Tome of Rage - I have heard that only FIVE of the shadow variant exist. I am one of the five with one but I haven't seen others with it. The other two (Prismatic and Divine) I have seen on two to three people but RARELY the shadow one.

• Wings of Summer/Winter - Barely see these around anymore. Winter is less common than Summer however if I'm right.

• Prismatic Ankle/Shoulder Boosters - Rumored to haven't been unboxed but heard that one of the pair may exist.

• Slippers - Don't know but seen one pair of Skolver around on a friend.

• Frenzy Pauldrons - A lot of talk that these may exist but have never been seen.

That's all the ones I can mention since these fit into the requirements of being rare as heck. In my opinion these are rare but for others may not be so the list may not be technically accurate depending on how often these items are seen so calm down lol. Also I may have missed some items and I apologize since there's a ton of them but these are the most rare imo. I guess I can mention some battle sprites as well:

• Drakon (Gun Pup): Only two people I know have them but if may be true that there aren't anymore unboxed ones left as stated above. The Anniversary boxes may give one a chance to receive the event box that contains the pet but even then the chances to get it are incredibly low.

• Maskeraith (Snarblepup): Only seen two others with them but possibly more may have them, rarely seen however. I possess on.

• Maskeraith (Spiraltail): Only seen one person with this pet. Had one before but sold it.

Now for the costumes and it may be incomplete since there are tons of them out there but bear with me:

• Generation 1 Rose Sets - Hardly anyone has these and technically Black Rose is slightly rare than White Rose and Red Rose is a little more common. I have both Red and White Rose.

• Prismatic Rose Set - Also rare and seen a few people with it.

• Bombhead Masks - The ones you get as a chance once you bribe King Krogmo, not the Krogmo Coin ones. Back then when a lot of people bribed him to get them they were somewhat common but now they're not as much anymore since not a lot of people waste energy in bribing nowadays.

• Sniped Stranger Hat - Rarely seen anymore but some people have it.

• Impostoclaus Hat/Winterfest Coat - Santa Claus set that has been unboxed the first time it was released and been selling for high prices until the second time it was put on Supply Depot which ripped those sellers off; rarely seen and past Winterfest events it was still uncommon. I have the set.

• Storm Dragon Helm/Armor - Heard that only one set exists but I dunno lol.

• Gun Pup Helms - Hardly see these anymore and the Love Puppy one doesn't count.

In terms of promo events, it depends on the person who sees which one is more rare than the other. Personally I say the ones that came before the others are more rare such as Hunter, Surge, Ancient, Gremlin, etc. but it depends so yeah. Plus the Anniversary event makes it so you get a chance at one of the past event boxes so it evens the odds on which is possibly rarer.

Apologize for the possible wall of text but hope this list helps. Cheers!