So what's the most technically complicated chess variant?

In My Humble Opinion
1

Obviously chess has its nuances, vast indescribable nuances. I doubt I could beat anything near a grand master, but at the same time you can reliably teach a five year old the basics (whether they decide to FOLLOW your seemingly arbitrary rules is a different matter entirely of course :p). But recently I looked into Shōgi, I knew it existed, but I never bothered to look into it until now. I figured it would just be chess with a couple pieces moved around or something. I was wrong, it looks fun. It hardly makes my head spin, but it seems at least technically more complicated.

By technically I mean there are a handful of more “basic” rules to follow, between dropping captures and promotion. It’s not that much more complicated just stating the additional rules, but it definitely looks like it adds a bit.

As far as I can tell, as Chaturanga got spread it broke off into a vast myriad of related games. Close enough you can see the relations between them, but sufficiently different that you can’t just pick up one by knowing another. Which leads to my question, which of these branches is fundamentally the most complicated. And by extension (I realize I’ve almost written a GQ post here), which do you find the most nuanced and complex, regardless of basic rules? (Some games have tons of rules but very few are ever invoked, leading to simple games regardless of the fact that they seem intimidating)

I wasn’t originally going to include the stranger sub-variants of the “main” ones (i.e. that gem called Atomic Chess), but screw it, go wild with whatever variants you know.

2

Friends of mine at uni created an octagonal chess board for four players (in fact, almost certainly like this), although it may have been the equivalent 3 player board.

The rules for deciding the movement of pieces were labyrinthine to say the least - straight line moves could take an arc, diagonals were impossible to work out, and don’t even think of working out a knights tour.

I think only a few games were ever played.

Si

3

It’s not very technically complex, but it IS fun to play strategically (and since you asked for variants, i’ll allow it):
Kriegspiel

4

There’s a variant called Choiss. It starts with a two by two square and a bunch of tiles. The players take turns attaching the tiles to the squares to build a board of their own design. Then they take turns putting their pieces down on the board. After this set-up they play the game.

There’s a game called Knightmare Chess (based on a French game called Tempete sur l’Echiquier). Each player starts the game with a deck of cards he can use during the game. The cards allow him to make special moves that are outside of the normal rules.