A list of all of my Understuck tracks (there's no official list). 
Big shoutout to /r/UndertaleMusic for working out how the Undertale songs are made up. They're a big help for anyone hoping to make Undertale-styled songs.

(NOTE: Pieces denoted with a '?' are Understuck pieces not considered part of my personal continuation)

Understuck

When I heard something about a Crustacean and a Bonetrousle, I figured I'd make a "Nyeh heh heh!"-styled Crustacean. Gotta love when inspiration hits you, even if it's only a little XD
(Sorry if the name is terrible. It was either that, "HAH HAH HAH", or something a little less child-friendly)

-"Crustacean" (Homestuck, Toby Fox)
-Inspired by "Nyeh heh heh" (Undertale, Toby Fox)

Quick mention of Malcolm Brown, since the 4/4 styling of "Crustacean" (it's originally 3/4) was inspired by his unreleased arranges of that song

Understuck - ENTER KARKAT

(Loops: 2)
When I made "HEY, KARKAT", I didn't expect myself to actually make its "Bonetrousle" counterpart, but sometimes lightning does strike twice in the same place!
Side-note: Who knew accordions worked so well with Crustracean?

-"Crustracean" (Homestuck, Toby Fox)
-Inspired by "Nyeh heh heh!" (Undertale, Toby Fox)
-Inspired by "Bonetrousle" (Undertale, Toby Fox)
-SFX at the end sampled from "Karkat's Theme"(Homestuck, Toby Fox)

Again, I should mention Malcolm Brown for inspirations from his various Crustracean arranges. Most notably, "Cheer up, Crabface! It's Halloween!" It's an amazing arrange of Crustracean ^w^

Understuck - Crabtussle

(Loops: 2)
This started out fun enough, but didn't stay that way. Trying to keep things sounding true to the original while using the chosen songs started to get frustrating with the minutia I had to correct. That said, I think it turned out okay in the end.
Note: I chose those three songs because they, to me, were all Homestuck's main theme at one stage (even if "Skies of Skaia" is Skaia's theme and "Sburban Jungle" is Sburb's theme)

-"Homestuck Anthem" (Homestuck, Clark "Plazmataz" Powell)
-"Skies of Skaia" (Homestuck, Mark Hadley)
-"Sburban Jungle" (Homestuck, Michael Guy Bowman)
-Inspired by "Once Upon a Time" (Undertale, Toby Fox)

Understuck - A Paradox's Beginnings

(Loops: 2)
Yeah, yeah. This is basically a give-away in terms of fitting it in Understuck, but that doesn't mean it shouldn't be done. Even the little songs add up.

-"Homestuck Anthem" (Homestuck, Clark "Plazmataz" Powell)
-Inspired by "Start Menu" (Undertale, Toby Fox)

Understuck - Press Start

I'm not sure if this exactly fits, especially since Anbroids isn't really "joyful" while "It's Showtime!" is, but what if a Hal-ified brobot played the role of "Show Host" with ironic gusto? Maybe the rap-bots were special guests this time round? All I can say for sure is, "It's Bro Time!"

-"Anbroids V2.0" (Homestuck, Malcolm Brown)
-Inspired by "It's Showtime!" (Undertale, Toby Fox)

Understuck - It's Bro Time!

(Loops: 2)
When it comes to picking the songs, I usually think about which character would fit there and how they'd interact within the re-designed world. It wasn't a short process, but I settled on Roxy here due to reasons I won't go on about in this description (I'll answer question though).
As for the song itself, Chorales and Fallen Down are...well, let's say making it fit without sounding too dissimilar was a process. I hope it still makes you think of "A kindly person meets the protagonist and helps them on their feet".
(Sorry if it doesn't sound great. I enjoy composing somewhat, but I lack experience in editing/mastering)

-"Chorales" (Homestuck, Michael Guy Bowman)
-Inspired by "Fallen Down" (Undertale, Toby Fox)

Understuck - Gentle Descent

I know it's been ages since the last Understuck track and this is hardly a big track to come back with, but sometimes that's the nature of inspiration and motivation.
Either way, this wasn't meant to be a serious consideration of "Temmie = ???", but since the theme is shared by Annoying Dog and the two of them are easily the silliest characters in the game (sorry, Burgerpants), it kind of works out. As to what you'd find in a Trickster shop...
(MIDI Link: http://puu.sh/sOF7N/e313ff5112.mid)

-"Tem Shop" (Undertale, Toby Fox)
-"Trickster Mode", "Trickster Mode 2" (Homestuck, Toby Fox)

Understuck - Trickster Shop

(Loops: "2")
Okay. Before we get onto anything, a couple of things:
1. (Another Megalovania?) Yeah. Another Megalovania
2. (But isn't Megalovania already a Homestuck song?) It is. This was really just a spectacularly silly idea that I went with because "Why the heck not?"
3. (Some parts feel like they were left in from your other one(s)) 
A) This used V2 as a base, so that's why it will probably sound very similar (this wasn't an entirely serious project)
B) A couple of little things were left there intentionally because they added a certain something to it

Now, as was mentioned above, why did I "homestuck-ify" a song that was already in Homestuck? Does it really count as Understuck? The simple answers to them is "It doesn't really matter". The idea was spontaneous and lacking any real sense, but I went with it anyway. It probably sounds rough as a result of that though. The reason it's labeled "Understuck?" is because it's not intended to be part of my personal continuum of Understuck (though I'm still think about Vriska == Chara). It was simply meant to be silly, and so silly it was.

On with the song choices and such. Yes, I used the same motifs I used in "A Paradox's Beginning". This is somewhat conflicting when one considers how [SPOILER]"Once Upon a Time"'s motifs were used in various places, most notably in "Undertale" and "Hopes and Dreams".[/SPOILER] I somewhat chose them on purpose, but mostly because they are the three themes I associate as Homestuck's themes most. The placement of Spider's Claw/Vriska's Theme and Sunslammer was because of its placement in Homestuck's "MeGaLoVania". The weird transition between loops was just a silly idea I kept, 'cause it's still Megalovania XD

Apologies if you don't really like the song or it's messy/badly processed. To be truthful, I got a little bored of fixing it and it wasn't meant to be entirely serious. With that aside, enjoy if you wish

-"Homestuck Anthem" (Homestuck, Clark "Plazmataz" Powell)
-"Skies of Skaia" (Homestuck, Mark Hadley)
-"Sburban Jungle" (Homestuck, Michael Guy Bowman)
-"Megalovania" (Homestuck/Undertale, Toby Fox)
--"Spider's Claw" (Homestuck, Toby Fox)
--"Sunslammer" (Homestuck, Seth "Beatfox" Peelle)
[Which was apparently an arrange of "Sunsetter" by Toby Fox]

Understuck? - Megalovania: Skaian Vengeance

(Loop: 3)
Another small track, but each track has its place and that includes Your Best Friend too. I had tried to cover the song out of fun/practise before but it was surprisingly tricky to sound accurate. I managed to figure it out for the most part (again, thanks to /r/UndertaleMusic for some assistance), and also decided I'd quickly make an Understuck version for it. 2 in 1, hey?

Why Terezi for Flowey/Asriel? A lot of my headcanon formulating for Understuck looks at the pairs and how they could work while still maintaining a similarity to Undertale's original story and relations. There are ones that seem obvious (Meenah for Undyne?), but don't quite fit in my mind. Then there are ones that are headscratchers (who'd be Frisk? Chara? Asriel?) and ones that have a few good choices (Sans = Aradia/Terezi/Dave).

I decided Terezi in the end, though, because I feel like Vrisrezi's dynamic could very well fit into Chara and Asriel's own dynamic:
-Vriska believing the plan to grab 6 more souls was the right way to go about it
-Terezi being uneasy but going with it at first
-Vriska wanting to destroy the humans but Terezi believing it's just plain wrong, stopping her at the last moment
-Terezi still wanting Vriska after all this time
There'd still have to be some changes here and there, but I can imagine Vriska wanting power and believing that was their purpose for revival (she decided she was the one who had to take English down before, so it makes sense, kinda)

Heheh, whoops. I kind of went overboard in the analysis, but it gives you a little idea in some of the (over)thinking I do. I'm happy to hear other headcanons and ideas of your own Understuck too. Who knows? Maybe it'd translate too well and I'd have to take it on too XD

Songs:
-"Lemonsnout Turnabout" (Homestuck, Toby Fox)
-Based on "Your Best Friend" (Undertale, Toby Fox)

Understuck - YOUR JUST FR13ND

(Loops: 2) 
Hey, I finished it, so now you've got the whole track to enjoy! Original post (with edits) below:

It's another "silly" track (that is, it doesn't fit within my headcanon of Understuck; Dirk would be in place of Undyne), and it started spur-of-the-moment. I wound up putting some effort into it, though, and it's shaped up into something reasonably decent. At the very least, it'll be a good base for if I make a more intended one.

Aside from the fact that I don't place John here, I still think it sounds decent enough. Doctor doesn't seem to lend itself to the second half structure-wise, but it's too fitting a song to not put there. In the end, while I kept Doctor during the transition, I switched up to Penumbra Phantasm (remember "Savior of the Waking World/Dreaming Dead"? The two songs have history together). It managed to actually sounds pretty neat IMO, so there you have it.
Despite the effort put into it, it's still not actually part of my personal continuum of Understuck. Still, it was a pretty fun song to work on at times.

A big shoutout to /r/UndertaleMusic for their efforts in pinning down just what soundfonts/instruments are used within each Undertale songs. Without them, I wouldn't be able to make these songs sound even half as accurate sound-wise (the piano-sound at the beginning of this is one example). If you ever want to make Undertale-styled songs, that's definitely a good place to start

Song:
-"Doctor" (Homestuck, George Buzinkai)
-"Showtime" (Homestuck, Malcolm Brown)
-"Penumbra Phantasm" (unreleased, Toby Fox)
-Based on "Battle Against a True Hero" (Undertale, Toby Fox)
(Trivia: Whenever I see that song name, I think of "Battle Against a True Heroine", since it is Undyne being the hero. Either works, I suppose)

Understuck? - Battle Against a True Heir

(Loops: 2)
Apparently, I'm on a roll with these things 'cause I've got another one of these completed(thanks again, /r/UndertaleMusic). Another simple track, but also another character. I've wanted to get one out for him for a while but I never really got around to it until now.

When I originally picked Karkat out for Papyrus, I immediately picked Dave for Sans. Sure, Terezi makes for a decent Sans and Aradia's 'maid' of time, but Dave just feels like a much better fit. Namely: He wouldn't let anyone hurt Karkat, even if he's such a nuisance to him. Whether you see them as best bros or a couple, they still fit the dynamic really well. Then you've got Roxy as Toriel, and Dave has famously gotten along with her in a way that's laughs for everyone. He might not be into physics like Sans is implied to be, but he can still drop science on ya (heheh). He's also a pretty likeable guy too, so there's that.

I'm not sure what the next track might be, but I know it's not Heartache 'cause it's a lot more complex than it first looks. If anyone's got ideas on what themes certain areas should have, I'm all for them.

Songs:
-"Atomyk Ebonpyre" (Homestuck, Toby Fox)
-Based on "sans." (Undertale, Toby Fox)

Understuck - sup

(Loops: 3)
Earlier, someone had made a version of Memory for Understuck using Terezi's theme as the base. Now, while it was certainly neat to see it, I had to go make my own because:
1) I wanted to add my own version of the song to my growing list
2) Memory uses "His Theme", not "Your Best Friend" for its melody.
So 'voila'. You have Memory using "Crystalanthemums" (or, more related to Terezi, "Crystalanthequins").

Why that song? Isn't it more associated with Vriska (or Aradia, depending on how you swing it)? Well, the way I look at Memory (and all of the themes that use it) is that, while it belongs to Asriel specifically, I see it as more referring to his relationship with Chara (he believes you/Frisk are them until after your fight, and His Theme doesn't make a re-appearance after the fact, which is right when he learns you're not Chara). It also fits really well, so there's that too &gt;w&lt;''

(Apologies if it doesn't sound too accurate. Apparently, it's more tricky than it looks)

Songs:
-"Crystalanthemums"(Homestuck, Alexander Rosetti)
-Based on "Memory" (Undertale, Toby Fox)

Understuck

FlareDragon