I cannot remember the UKK's off of the top of my head but I do know that gamefaqs.com has all the codes you could ever want for any game, including UMK3.

I tried but i'm not gonna press like lpX8 myself and stuff. Plus, I tried before and it doesn't work.

I'm afraid you will have to press all those buttons.

Mileena:
2226422264

Ermac:
1234444321

Sub Zero:
8183581835

if you hold UP while pressing a button on any Kode screen (kombat or UKK), you will cycle backwards through the symbols. So if you don't want to press LP 8x, you can just hold up and tap the button twice.

And remember to think of the buttons as a "W" when entering the UKK.

UKK slot 1: Player 1 HP
UKK slot 2: Player 1 LP
UKK slot 3: Player 1 BL
UKK slot 4: Player 1 LK
UKK slot 5: Player 1 HK

UKK slot 6: Player 2 HP
UKK slot 7: Player 2 LP
UKK slot 8: Player 2 BL
UKK slot 9: Player 2 LK
UKK slot 10: Player 2 HK

Also to save time you can hit multiple buttons at once... like for Ermac I start by hitting every button once. Then press all the 2,3, and 4's. For my third tap I get the 3's and the 4's. Then just one more tap to get 4444. Of course if you are using a keyboard that would limit your use of this technique, in that case just hit the keys really fast I guess. If you just stick at it I'm sure you can get it.

For human Smoke try holding the buttons as early as possible and don't let go until after Khan says FIGHT. And holding "back" is a relative term, make sure you hold LEFT if you are Player 1 and RIGHT if you are player 2.

all th codes work, tested them last month on the arcade near my high school

I'm using MAME and still no.

Then either you are doing something wrong or there is something messed up with your copy of Mame. The only other thing I can think of is that you'd be trying online or something. If you unlock them offline they are not there when you play online. Every time you play online you have to unlock them again.

Is there a cheat file for mame 0.95 or hacked mame 32K? I bet i'm doing something wrong then.

I have tried a few different versions of cheats for mame to unlock those characters but haven't found any that work. The other option is to get a copy of the npram file from someone that unlocked it already. That has worked in the past.

i got MK3 and UMK3 on MAME ... they work trust me to unlock the secret characters.

make sure u got your controlls setup properly... and make sure u enter the codes correctly.

Do I need 2Players? Cause I can't do that.

no, you just need to configure the controls for both players because as you ́ve seen the codes use both controllers