@billy Speaking of Game Gear, let‘s not forget Janet Jackson’s (unintentional?) cover of Sonic GG's Bridge Zone:
And of course The Jetzon's Hard Times which I think is the reverse of this. A vocal track turned Ice Cap:
@billy Oh good call, though I can't see that animation without hearing “SONIC BOOM SONIC BOOM SONIC BOOOOOOM” in my head. I loved that song so much that as a dumb clueless kid I would always check the CD racks at music stores for a “Sonic” tab on the off chance that they had a Sonic CD OST CD (I guess??). I developed a vague distaste for this band I had never heard of called “Sonic Youth” that always seemed to occupy that spot instead.
I just thought of one that’s kind of an inverse. I fell in love with this Goonies 2 song after hearing the cover by The Advantage…
https://youtu.be/7BLw91xljQ8
https://youtu.be/0kIvSA6-Y6s
…only to find out many many years later that this is a Cyndi Lauper song
https://youtu.be/LxLhytQ67fs
https://youtu.be/amW-WikUy2I
here you go, lol
https://youtu.be/mnTVTutstcI
Also you can kind of just search anything “vocal” on youtube to find stuff like this.
Bloody tears 
I‘ve got bloody tears
Bloody tears🎶
They’re so bloody bloody🎶
53 Stations of the Tōkaidō - Momoko Song
As made famous by GCCX , the lyrics to the heavily repeated song from the game are listed in the strategy guide.
https://www.youtube.com/watch?v=qbwo_9QieXE
あ～と江戸まで何十里～♪
あ～と江戸まで何十里～♪
じゅ～う里～♪ は～ち里～♪
待っててくれ 桃子ちゃん～
オイラの花火が おみやげだ～♪
江戸はまだまだ まだまだ遠いのか～～♪
Ato Edo made nan jyu ri~♪
Ato Edo made nan jyu ri~♪
juu ri~♪ hachi ri~♪
mattete kure Momoko-chan~♪
oira no hanabi ga omiyageda~♪
Edo wa madamada madamada toi no ka~~♪
How many more miles until Edo～♪
How many more miles until Edo～♪
10 miles～♪ 8 miles～♪
Please wait for me, my dear Momoko～♪
My gift to you is the fireworks above～♪
Edo is still, still, still, still far～～♪
https://www.youtube.com/watch?v=1QFtYRKy8T8
I just remembered that the Japanese version of Astal's opening has lyrics which were removed for the American version:
https://youtu.be/b6fOrsdgqlY
https://www.youtube.com/watch?v=VNV5zBxV-lQ
I'm not sure if this is ever used in game, but it's probably my favourite thing off the OST. All items should be explained in song.
How could I forget…
https://youtu.be/C8vz186pjY0
@thebryanjzx90 exactly how I sing it too 
Thinking about this recently…
Hadn't listened to it in over a decade, yet every so often the lyrics come to mind
@captain oh you mean the famous system of a down bootleg track?
Takenobu Mitsuyoshi of Dayona USA fame added lyrics to Ryu's theme
And here's a vocalized Guilty Gear album, to uh, some effect
this rules
wow why wasn‘t this in ssb like his f-zero theme?
can mitsuyoshi just keep doing this for all games please?… like he can’t be beat.
Imagine getting to the last level of a space shooter or a platformer like contra and suddenly.... mitsuyoshi singing as the skies light with flame
The iconic theme song to the Fire Emblem series and heavily featured in the Super Smash Bros line of games, has canonical Japanese lyrics originating in ads for Fire Emblem: Shadow Dragon and the Blade of Light that tells you how to play and that you're probably going to suck at it:
https://www.youtube.com/watch?v=9HB7JYZhSzg
>
Fire Emblem, tough simulation
> When you‘ll begin playing it, you won’t be able to sleep anymore
>
>
Although you should surpass your opponent, a critical hit !
> When there‘s nothing more left, Life Staff, when you’re in a hurry, Relife Staff
>
>
Both in attack and defense, don‘t press unwisely,
> And don’t let anyone die !!
>
>
Fire Emblem, tough simulation
> When you‘ll begin playing it, you won’t be able to sleep anymore
>
>
Put too much effort on powerful people,
> And your warriors on the whole will only be novices
>
>
Fire Emblem, tough simulation
> A tale of love and courage
>
>
Fire Emblem, tough simulation
> Come and win bravely !
>
>
When things become dangerous, run like the wind !
> Those who get cocky will put themselves in peril
>
>
Fire Emblem, tough simulation
>
But maybe they thought it was too embarrassing so they translated the lyrics into Latin for Latin speaking audiences.
>!
>!
https://www.youtube.com/watch?v=hg-kK-aFYsM
>!
>! >
Fire Emblem, companions walk
>! > The endless path together.
>! >
>! >
In the wavering shadow of spite,
>! > Our home is faced by the oncoming spear,
>! > Engulfed in flames.
>! >
>! >
I keep that unforgettable day in my heart
>! > And now rise up together with my companions.
>! >
>! >
Fire Emblem, our bond shall be never broken.
>! >
>! >
We hold fast to protect tomorrow
>! > And the one who awaits our return.
>! >
>! >
Fire Emblem, light gathers on the flag we unfurl.
>! >
>! >
Fire Emblem, we gaze upon the multitude of stars,
>! > Gripping our blades.
>! >
>! >
If we do not bring light to the darkness in these lands,
>! > The shooting stars will soar over a wasteland.
>! >
>! >
Fire Emblem, on whom does the morning sun shine
>! > As she climbs over the edge of battle?
>!
Then they finally localized it into English for Fire Emblem Heroes and there was also a totally different version for Tokyo Mirage Sessions.
>!
https://youtu.be/xfTuQmE35JM?feature=shared
>!
>! >
Fire Emblem
>! > Your spirit shall shine
>! > Across the generations
>! > Now and for all time
>! >
>! >
Fire Emblem
>! > Heroes, bring us hope’s light
>! > Journey from distant worlds
>! > To still the coming night
>! >
>! >
With sacred relic at your side
>! > See our champions fall from on high
>! > In this land where timeless heroes live
>! > And their legends never die
>! >
>! >
Fire Emblem
>! > Brave heroes of the ages
>! > With my design and your hearts true
>! > We’ll start anew
>! >
>! >
The end is within our reach
>! > Take up my fight as I beseech
>! > To kingdoms ravaged by senseless war
>! > Bring us peace forevermore
>! >
>! >
The strong, the weak, the brave, the meek
>! > All shall fight for the light we seek
>! > Hear my voice, brave heroes, hear my plea
>! > Come to me, come set us free
>! >
>! >
Fire Emblem
>! > Your spirit shall shine
>! > Across the generations
>! > Now and for all time