X-Men

When they show a shot of the outside of the submarine after Storm, Wolverine and Omega Red have gone in it, you cannot see the mini sub.

When the nuclear warheads are first shown, they read "Nemesis" in Russian letters, misspelled as "Nemisis". When we see them next on the screen from Omega Red's point of view, the writing looks different, with at least two letters changed to Latin alphabet N's.

This episode is a sequel to season 2's "Red Dawn", and features the final appearance of Omega Red.

When it shows the 3 military jets flying to the submarine in delta formation the one on the right of the screen is way smaller than the one in the middle yet the smaller one's wing overlaps the bigger jet.

When showing the submarine "listing", the mini-sub, which just surfaced, is shown to be still attached to the sub.

The mini-sub front window, which normally shows the green sea, shows blue sky and clouds when Storm talks Wolverine out of attacking Omega Red.

Wolverine's belt is brown when agreeing to go along on the mission.

When ripping off the hull of the sub, Rogue's feet are missing.

The submarine ends up landing on a ledge almost identical to the one it'd been resting on earlier, miles away.

All the main characters appear however, Jubilee, Rogue and Storm do not have any lines. Gambit doesn't technically have any lines, but you hear him grunting.

Onscreen title includes "The" at the beginning, despite the first part lacking it.

When the group enters Magneto's Arctic base, they appear to be walking in place for a few seconds before the scene continues.

Just before the group enters the empire state building, Forge's mustache kept appearing and disappearing.

Cyclops and Jean Grey do not appear in this episode. Gambit and Rogue appear, but do not have any lines.

Cyclops, Gambit, Jean Grey, Jubilee, Rogue and Storm do not appear in this episode.

The Scarlet Witch appears for the first time (due to having been part of Force Works on the Iron Man cartoon series which aired until just prior to this show's debut). Professor X and Wolverine seem to know who she is, suggesting that she's been active off-screen (of course, she had a cameo in season 2's "Repo Man"). She'd later be part of Fox Kids' final Marvel Comics team toon series, The Avengers.

The High Evolutionary makes his first (and only) real-time appearance, after having been shown in a flashback in "Savage Land, Strange Heart (2)". He (or a reasonable facsimile) would later take a more prominent role on the Marvel animated series, Spider-Man Unlimited.

Forge has a nonspeaking cameo in this episode.

Magneto will next appear (along with Quicksilver) in "Phalanx Covenant (2)".

When Wolverine is changed into the large animal version of his moniker, his costume is shredded, particularly after he's changed back to normal. But when Magneto flies away at the end of the last scene, Wolverine's costume is intact and includes long yellow sleeves!