The All-Seeing A.I.: Much like the original series, the AI will most likely be more aware about its surrounds and nearby items than most human players would.

Art Evolution: Very clear. From directly ripped and MS-painted sprites in the original game, to ripped-but-tweaked sprites in the early sequel demos, to every character having entirely-custom, uniformly-styled sprites.

Home Stage:

In the first game, despite its many characters, there were only five franchises having stages of their own. Which were:

Peach's Castle and Mushroom Kingdom II for Mario.

Temple for The Legend of Zelda.

Dreamland for Kirby.

Pokmon Stadium for Pokmon.

And Emerald Hill Zone for Sonic.

In the second game, due to the larger file size limits, every franchise with a playable character gets at least one stage based on their series.

Meteor Move: In 1, every character's up attack and down aerial can dunk opponents. This can be difficult to pull off, as the opponent needs to not only be airborne, but also either moving slowly or not at all. 2 has meteor smashes and spikes, with the same functionality they have in the official Smash games, but a few characters don't have access to either.

Platform Fighter: Much like the original Smash Bros. series.

Retool: There were two notable ones in total:

The transition from Flash to Flash 2 completely rebuilt the mechanics and the focus from the ground up.

Demo v0.7 of 2 was the official turning point from "anything-goes fangame" to aiming for professional quality.

Ring Out: Just like in the original Super Smash Bros. games.

Stock Footage: Present, but diminishing rapidly.

The original didn't have any of its own sprites, save for the Pokmon Stadium stage. All others were taken from The Spriters' Resource. The earliest demos of 2 also used ripped sprites; Lloyd and the Sonic characters used the same sprites as in Super Smash Flash, Sora was ripped from Kingdom Hearts: Chain of Memories, and the anime characters were ripped from Jump Ultimate Stars. Gradually, however, more and more of the characters began getting entirely custom-made sprites, to the point where the series is now fairly well-known for its quality graphics.

Amusingly, the earlier, lower-quality custom sprites for Link, Ness, and Mewtwo*He was planned for the original, pre-retool roster, but is now uncertain. later became stock footage when they were salvaged by Super Smash Bros. Crusade.

The original also didn't have originally composed music (save for the How to Play track), ripping songs from Melee, the "Smashing... Live!" album for Melee, and in one case, The Matrix Reloaded. 2 also used ripped music from various sources, including remixes from other composers, before gradually replacing them with the dev team's own remixes and even giving SSF2 its own theme to use as a Leitmotif for all Smash-related content.

Ultimate Showdown of Ultimate Destiny: The first game is this, full stop, with characters like Blade and Mr. Incredible. Traces of this sentiment remain in 2, at least in development; Cleod thinks that the anime characters fit in well (although the other developers don't), and he has a personal soft spot for the Original Characters who were planned to be in but had to be removed due to losing contact with their creators.