Gwent is a 2 player collectable card game from The Witcher 3: Wild Hunt video game. PLayers duel with other characters using over 150 playing cards with multiple combat styles, heros and spells.
The Witcher Gwent Card Game has:  4 Sets of Gwent decks, 4 Gem Life Counters, 2 Individual Play Mats, 4 Card Fraction Discs and Instructions.
The four "sets" or decks of cards are the four factions, when chosen as active deck, provide a different bonus during the Gwent match:
Nilfgaardian Empire: Wins any round ending in a draw
Northern Kingdoms: Grants an extra card upon winning a round
Scoia'tael: Decides who takes the first turn
Monsters: Keeps random Unit Card out after each round
Each deck consists of:
Unit Cards – These are your bread and butter. They make up the bulk of your deck. Think of them as the pawns in a chess game.
Leader Cards – There are only sixteen leader cards. Four representing each of the four main factions (decks) Northern Realms, Nilfgaard, Scoia’tael and Monster.
Special Cards – These are mainly weather cards that have a negative effect on a row of troops: Close Combat, Ranged or Siege. Some weather cards counter the effects of all-weather cards, effectively making the use of a weather card null and void, so be wary when playing your weather cards, your opponent may have a trick up their sleeve.
Hero Cards – These cards often have a high point value and are immune to the effect of all cards and are unique to their faction deck type.
Neutral Cards – These are the same as Hero cards but are not tied to a faction deck type.