Yeah, my subsequent playthroughs have employed many new tricks that I was not aware of in the year 1999.

And here I am, thinking Fire Emblem is a bit too complicated.

There's also the mechanics of the legendary "8F" item. In Red and Blue, this item can do *anything*; you just need to have your inventory spell out the machine language instructions to do what you want.

Worth noting that:
* The item's name "8F" is not a hex code; it means "8th floor".
* Actually obtaining this item requires other glitches, most notably item underflow (which also makes it possible to warp to the Hall of Fame room).
* Of course, you can't literally do anything this way; you can't, for example, do anything that could not be coded into a ROM hack of the game. But still, there's a lot you can do, including catching Mew and replacing the game with Pong.

Card-based mini-games. I never liked those, but I especially hated FFVIII's Triple Triad. I mastered it (frankly, out of spite) but it left me permanently burned out on card games.

Fishing in most games, especially MMOs.

Certain Zelda based mini-games. I like many of them, but others I can't stand. In one of the Oracle games these's a Simon Says dance game to earn a boomerang. I never had patience for that so I've never completed it.

I tend to dislike mini-games but every now and then I find one I enjoy, such as the snow boarding mini-game in Final Fabtasy VII.