For me, It's either-

MK2 because I could never usually get past the first five guys.

or

MKSM because I can never beat the Triple Trouble at the end.

Maybe it's my fault, but the story mode in MKDA and MKD seem really hard (almost impossible) due to those style-changing combos required to advance the story... I'm probably doing it wrong, I don't know, but it's really frustraiting.

Mortal Kombat 2, doubtlessly. I mean, females are as cheap as CPU can get, and of Kintaro I won't start...

Konquest mode in Deadly Alliance has it moments and in UMK3 Jade and Shao Kahn can be near impossible to beat. In Deadly Alliance and Tournament Edition on the GBA, Shang Tsung and Quan Chi can both prove to be pains to beat (especially in Deadly Alliance because you don't recover health in between rounds. I really dislike Endurance fights), but I'd have to say that MK 2 is pretty hard. I have trouble against Raiden and Baraka, and I can never get past the third fight.

Mortal Kombat 2, It took me a good 1-2 hours to beat that game. The AI is a pain in the butt.

yeah mk2 is hard

MK2 is definitely the hardest Mortal Kombat ever.

Actually every MK have one or two stupid character(s)

MK:Goro

MK 2: Kintaro and Shao Khan

MK 3: Motaro and Shao Khan

MK Deadly alliance: Moloch...In finnish it`s mean dick if you take Molo(ch) those letters away...So Moloch is a dick

MK Deception: Onaga...Not so hard to beat!!!!

MK vs DC: Dark Khan..Really stupid charactrer if you ask me..It seems that ideas just ran out..And the the Dark Khan was born...stupid character...

MK shaolin monks:Shan tsung, kintaro and Shao Khan...stupid, too hard...
But the easiest way to beat them is shoot hats and fire meat balls,,,

Baraka rules.....

MK2 and MK Deadly Alliance

MK games are harder at the first tries.Once you learn the attack pattern of the machine they are a piece of cake,there are cheap ass strategies for every game.

MK2 on the home consoles. It seems they bumped up the difficulty to max. The AI will suck and then out of nowhere pull out a 5 hit kombo on your ass.

MK:2 A.I. is pretty ridiculous to this day. I still manage to get to Kintaro no matter what though. Now once you've reached that beast. Prepare your mind for some serious mental abuse. Accept yourself being cheated when two of Kintaro's hits can either equal a victory or up to 75% damage! WTF. Can't complainl; Umk3 is the best stable 2D fighter from MK. Which is probably why they released it via X360 online baby!

MK3/UMK3/MKT because the combos are mostly too hard to do that I had to use cheats for it. Plus, a lot of characters are just plain hard to play as and play against.

i can just barely beat mk2 but my friend is the best at fighting games he can beat it easily with reptile and subzero in one try without losing a single match.

I agree MK2

MK2, two big bosses with Shang Tsung before them.

But... has anyone noticed with the old school games, they beef up the difficulty each new fight... unless you lose, then they tone it down to keep you going?

For me, it's MK2 & UMK3

UMK3 only because of Sonya or Jade, everything else fairly easy I guess...

I'll have to go with UMK3, depending on who you pick. Most characters have silly AI glitches that can be exploited, but every so often they just don't work, and you receive a major beatdown - having someone with a teleport makes things very easy. MKII can be tricky but patience always perseveres, every single enemy minus the bosses falls for the backwards jump trick.

MK2 is really hard even the Kombo Khallenge in MKvsDc is hard having redonkuous wierd timing to beat them.

For me, it's either MK2 or Jade in UMK3 because she counters everything I do. I used to have a really hard time beating Shao Kahn in UMK3, but now I can beat him easily with Scorpion.

I have the Shaolin monks secret mk2 and I turned it off at Shao Khan due to frustration. That's the only mortal kombat I haven't beat yet.

MK2 (ps3) for me. Spend ages trying to defeat Kintaro then sobbing with happiest and exhaustion you stumble into Shao Kahn and he just hammers you to death with ease. I've completed it exactly once..my nerves couldn't take a second pop at it. Love it though.