Assassin is a special multiplayer format.
- Take 2 cards for each player, for example in 5 player game take 2 of each basic land type.
- 1 card is given each player face-up as their “face” another is given face down as their target.
- Every time you defeat your target, you get their target.
Read more:
https://mtg.gamepedia.com/Assassin_(format)
Alternative version or as how we played it:
- Each player can only attack their target, with spells you can target anyone.
- After you defeat your target you can attack anyone
- Last one standing will win.
MTG blog 