A small update. I noticed a problem with the bottom screen image, so I just...fixed it? I just decided to change the image completely for one that I like a little bit more...yeah (also, the “launch” sound is a bit louder, everything else is the same).
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Credits:

Mario, Luigi (SMA2) and backgronds sprites by: Mister Man. Princess Peach sprites by: Asaki (taken from the his color restoration patch of SMA2 on RomHacking). Yoshi sprites by: A.J Nitro and thejohnston7. World map border by: DogToon64. Miscellaneous by: Nintendofreak106 and SuperExperience. Music by: MercuryPenny. SFX by: Deezer.
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Changes and other things:

-Colors (I think it's the most noticeable change of all, now it has the original colors of the SNES game!)

-Bottom screen.

-yoshi and Luigi's sprites were painted by me using the original SNES colors (although, for Luigi's sprite, I took a color from asaki's color restoration romhack of SMA2, I think that one color is not present in Luigi's sprites in SMAS+SMW).

-The logo is an unused/early version of the game logo that I like :). (taken from Super Mario Wiki).

-Music (it's the same as the original theme but with the soundfont of the original SNES game) by: MercuryPenny on SMW Central.

-SFX (now from the original game, by Deezer and taken from “The Mushrom Kingdom” web page).

-The dinosaur land artwork (well, only the Yoshi's island, a little bit of donut plains & chocolate island parts) now has color! (I think it was a poster or something that came with the GBA game, I don't remember if it came in the original SNES game).

Title screen (SMA2) - Yasushi Ida, Taiju Suzuki (recreated by: MercuryPenny)