All of these images were taken from something called "X-Men: The History", a Japanese promotional video from 1995. The video shows a version of the game that has some differences compared to the final:

The X Power gauge displays "level 0". In the final, there is no level 0, the lowest the gauge can be is level 1. Also Wolverine is doing his Hyper X move but his X Power gauge is still full.

The yellow explosion effects were changed to red for the final. The explosion at the bottom was also changed to where the laser bounces in the final version.

A small change is that some lower case letters were changed to capitals in the final. For example, "level up" in this early screen would become "Level Up" in the final.

The background for this stage shows the sky during a fight, which never happens in the final. In the final version, the sky only appears at the very start of the fight and when the last round is over.

The glass also cracks for no reason in the video -in the final it starts to crack due to the pressure as you move further down into the sea.

Sentinel sending in 4 mini-Sentinels at his opponent, in the final version he only sends 3 mini-Sentinels per attack.

This is a slightly different title screen. The Marvel Comics logo is in a slightly different place, plus the screen doesn't show the version number of the game.

In the video, Omega Red manages to jump that high with a super jump, but when I tried it in the final version he can't get anywhere near that height.

Wolverine using his mutant healing X ability move even though A) his health is full anyway and B) his X Power gauge is empty!

This says that Colossus' Hyper X was the first attack, but Cyclops has clearly already taken some damage already (the red on his life bar is how much damage Colossus' Hyper X has done).

At one point in the view, Spiral is shown super jumping upwards leaving Psylocke down below. The words "S.SPECIAL" briefly appear, I've no idea what they mean and they don't appear. The "1P" arrow is also pointing downwards, in the final I've only ever got it to point left or right.

Iceman's ice beams don't travel travel off the screen in the video and fizzle out early whenever he is shown doing them.

Colossus had thrown Sentinel and damaged him first, but Sentinel is shown hitting Colossus afterwards and getting the "first attack" message.

Sentinel shooting a laser from his mouth whilst ducking. In the final he shoots a missile from his mouth instead.

A few seconds later in the video Sentinel is shown shooting a missile from his mouth whilst standing. I don't think he can do this in the final.

Blue explosion effects during Cyclops' Hyper X. In the final they are red.

When the video shows Magneto, the words "Round 1" and then "FIGHT" appear far too early -Magneto is still floating down! In the final the fight won't start until Magneto is on the ground and has his helmet on.