Toby just released a linux build of the game. Linux build changes two things. The volume bug with Asriel's lamp was fixed and MASHING IS SIGNIFICANTLY EASIER

How to obtain the Linux build via Steam.

1: Start Steam
2: Update to Undertale 1.001 (opt out of the 1.0 beta by right clicking in steam > properties > betas). You can't use this on a 1.0 version. Your executable has to be 1.01. We lose 7 seconds between Papyrus skip and the wall hug in hotlands, but overall the mashing changes compensate for RTA.
3: Click this link steam://open/console
4: You should now have a new tab inside Steam named "Console". Might need to try the link a few times.
5. Type this into the console: download_depot 391540 391544

It should then say:
Downloading depot 391544 (116 MB) ...

And then once it's down downloading it'll say something on the lines of:
Depot download complete : "C:\Program Files (x86)\Steam\steamapps\content\app_391540\depot_391544" (224 files, manifest 3991795236625517204)

Then if you go into that folder you should be able to find a file named game.unx. Rename this to data.win and drop it into your Undertale folder (it has to be v1.01, not 1.00). We lose the Papyrus skip but mashing is significantly easier.

Save files in this version are left in appdata/local/UNDERTALE_linux_steamver

Batch file for Linux build
del "%localappdata%\UNDERTALE_linux_steamver\file0"
del "%localappdata%\UNDERTALE_linux_steamver\file8"
del "%localappdata%\UNDERTALE_linux_steamver\file9"
del "%localappdata%\UNDERTALE_linux_steamver\undertale.ini"
del "%localappdata%\UNDERTALE_linux_steamver\system_information_962"
del "%localappdata%\UNDERTALE_linux_steamver\system_information_963"
del "%localappdata%\UNDERTALE_linux_steamver\playerachievementcache.dat"
start undertale.exe

Debug offset is 725DDC(edited)

Technically it isn't faster, since Papyrus skip is impossible, a phonecall trigger is fixed in Hotland (before the first laser section) and the jump puzzle pause glitch doesn't work in 1.01. However I've tried this myself and it will DEFINITELY improve someone's mashing if they're typically an inconsistent masher.

I know this is what you meant, but it will be faster RTA for some runners, however not everybody.