My question is how do I get my replays in the default custom folder like '6 faces'. I want to get one into the replays folder

Iirc, they are picked if you just post it in the replays board.

1.They must be Beatiful
2.Awesome
3.Be in replay thread or acknowledged because of how awesome it is.
4.Pro.

Jim guessing hands must have to think that its worthy enough to be in there

There is two ways to get your replay there.

1. (Not completely sure, just based on a rumor)
Staff check the each attachment attached on the forum, and if they see a replay truly incredible, they'll make it a default replay.

2. There is also nabi sp competitions, in which you post 2 replays for a huge prize plus a chance to get your replay on the default replays folder.
It isn't annual, though.

Make a really really really good replay.

When do they usually host these comps? when a new version is about to be released or something?

usually if the old replays are simply getting - old, or when something new is about to release which will change the replays.

there is may 1 or 2 in the year. the replays just should show what everything is possible in this game.