not so wierd, to be honest.
it's black's strategy to let white develope a massive center, then attack it. black wants white to use as many tempos on pawn moves as possible in the opening , while black uses few pawn moves and developes his pieces instead. so he's ahead in developement. however whites center creates the illusion of white being better, but he will fall very fast if he doesn't play accurately.
I've won against players rated 2-300 higher than me using this strategy
Post opening oddities--things like main lines that break all the traditional opening rules, or yield unusual positions (tripled pawns, pieces moved and then returned to their starting positions, etc)!
Here's a fairly basic one:
One of the main lines of Alekhine's Defense: 1. e4 Nf6 2. e5 Nd5 3. c4 Nb6 4. c5 Nd5 5. d4. Black has moved his Knight four times (ultimately returning to a square he was just at), yet is still considered to have a playable position (36% winning chances in Chess.com's database)!