Discussion What are your favorite video game mods/hacks?

Some of my favorites:

- Various hard-mode mods for the Trails of Cold Steel series
The three currently available are all made by different people, but they're all great in their own right. Honestly, I might even recommend playing a blind playthrough with some of these mods on a lower difficulty because of how well they balance the games. There's a lot of stupid oppresively overpowered tools. With those nerfed, other fun options and strategies are able to take hold.

- Brawl Minus
A mod for Super Smash Bros. Brawl that attempts to balance the game. Except, instead of doing the sane thing and nerfing Meta Knight, they BUFFED him and then everyone else to that level. Also added in a bunch of characters like Mewtwo, Pichu, and Waluigi. It's an absolute blast to play casually because of just how much fun stuff every character gets.

- Super Mario Bros. 3Mix
A mod for Super Mario Bros. 3 on NES. Turns it into a brand new game with level themes based off of other games in the Mario series—even a bunch you wouldn't expect! New music, 3 hidden star coins in each level, revisitable worlds, secret levels, multiple exits, new gimmicks, A RIDEABLE YOSHI. Not to mention the levels is top-notch. It's the closest to Nintendo's level design I've seen a fan project come. If you have any nostalgia at all for the Mario series, this is a must-play. Assuming you obtain a copy of the SMB3 ROM legally of course...
I'm a big fan of randomizers especially for Legend of Zelda. Zelda Ocarina of Time: Randomizer is very good and has lots of really fun options to mix it up every time. And speaking of that, there's been quite a few new hacks for OoT though they are still very rare. Dawn and Dusk and Nimpize Adventure are both very solid if you played the original many times as I have. Dawn and Dusk in particular are very polished and also quite short, it's a good weekend Zelda experience. I personally hope OoT modding continues to become easier and more well documented. (They're doing a decomp project atm, I am excited for when it is finished to see what we get out of it).