Ok so here you go, Swapdust\Dustswap Papyrus' history and evolution. I wanna clarify 3 things over here: 
1. Counting both Swapdust and Dustswap as the same as long as they are Underswap Papyrus doing the killing and if they were created after swapdust.
2. Only the 3rd and 4th sprites are canon.
3. Takes are included here because they are frequently used, are original and have a good concept, have a chance of being "canon", and are so fanon that people use them a lot lol.

Ok so let's go to le explanation:

1. Underswap (popcornpr1nce): Just Papyrus. Nothing out of the ordinary.
2. Underswap (popcornpr1nce): Guys he put his hoodie on oh noes.
3. Canon Swapdust (FanFiccentral30): Yup, that's the canon design. Papyrus just has a red-orange eye. Deal with it.
4. Also Canon Swapdust (buttercupsticksntricks): Same as the last one but fanon. Also 2 eyes instead of one. You can consider any of these 2 your headcanon and have no problem.
5. Legcorn's Swapdust: He threw an orange penis at hos brother and died. Boohoo.
6. RallivSalado's Swapdust: Remember that one time where ralliv posted swapdust pap's with the dusttrust eyes, because I sure did.
7. "Dustbelief" Swapdust: Swapdust but with dustbelief eyes. Oh boy. This is the most common version you'll see out there.
8. Swapdust: Dust 'till dawn (Pixelbit0): Swapdust but in reverse. Basically, Papyrus respawns everyone you kill and steals ur LV :0. Very cool and original concept ngl.
9. Sawsk's Swapdust: This iteration appears in Sawsk's Dusttrust. Basically Dustbelief Swapdust but he doesn't Blue, Red, or a more characteristic orange anymore.
10. Underswap: Brain-washed (BadnessofTime): This was previously just swapdust. Honestly the chadest take u'll ever see. And it has originality what. Basically Swapdust but the design is original.
11. "Fanon" Swapdust: He just has yellow eyes. Moving on.
12. D4niztic's Swapdust: Pretty good take ngl. Concept is cool and all, but I would prefer it to stay as a take.
13. "Dusttale" Swapdust (ThePhilPlays): Swapdust itso Dusttale. Good enough to be canon tbh.
14. New Swapdust(?) (Anonymous): Possible new design for Swapdust. Basically fixes the canon design.

I'll maybe do a Phantom Sans later on, just to add up.
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Credits:
Undertale by Toby Fox and Temnie Chang
Swapdust by FanFiccentral30 (Tumblr account is RIP)
Other creators credited above

Ask before use and\or editing. Original AU creators may use the sprite for their AU freely.

Discord Tag: [Strawberry-Smoothie]#8995