Booster packs and mystery boxes in games!

Hearthstone.

Many free to play games in China.

Booze roullete/poker & women in real life lol (better spent that way ) ,gamblin in fail PAY 2 Win Cash-!%!# MMORPGs is fail ( even epic ones like Runes of Magic :( you will notice in-time ) :)

Mu Online i spent $20 for chaoscard platinum never got good sh*t

P.s. i don't play the game anymore

Battleblock Theater has randomized unlockable prisoners. It's lots of fun!

Defiance

Also, pretty much all loot chests in Borderlands are like "mystery boxes" as you never know what the hell's going to be in them.

Most online card games, tf2, csgo off the top of my head.

Counter-Strike has some mistery boxes....mistery HIT boxes.
You can never know where they really are.

The unlock system in Battlefield 4 is all kinda random boosters isn't it?

Rise of Mythos, its a/an -got to polish my english a bit- strategy/rpg browser game, it has cards, which represent units for the battlefield, and you can buy booster packs without spending real money, there are also a lot of random stuff there, like when you finish a dungeon, you get to choose 2 of 16 (or more) cards in order to get your reward, and those "stay online to get rewards" work with the same system. Its a nice game if you dont mind those kind of games (for myself i kind of hate most of browser games, but this one isnt THAT Pay2Win. It's playable without paying, at least i think so.

Star trek online

Mass Effect 3 MP and BF4

100% Orange Juice