The primary object of Killer Bunnies is to acquire carrot cards, one of which is revealed to be the winning "magic carrot" at the end of the game. This is done primarily through the use of bunnies, which allow the use of many in-game actions. Thus, the game revolves around playing bunnies and eliminating opposing bunnies through various means (some comical and some violent, but the game art never shows blood or gore).
Each player maintains a hand of five cards and a run cycle of two cards. In each turn, players may play one card. They are given the opportunity to purchase Cards from the market, use very special cards that are in their hand, or target weapons or cards at another player. Then the player's hand is replenished, and the player flips over the top card (which is a Run card) so that the card is face up and visible to all players. Then the player slides a face-down card up to where all the new cards are revealed. Then, the player draws a card to replenish their hand to five cards, and places a card face down on the playing surface.
Cards may be one of different varieties: "Run" cards are the basic type of cards, while "Special" cards are those that may be either played normally, or may be saved for later use when put through the run cycle. "Very Special" cards are similar, except that the player may choose to play the card out of turn, immediately from their hand. There are also the "Play Immediately" cards, which are played whenever they are drawn. Finally, "Kaballa Dolla" cards represent the monetary currency in the game, which may be used to purchase various items at the start of the player's turn.
The game continues until every Carrot card has been acquired by the players. At the end of the game, a stack of smaller carrot cards, each of which corresponds to a large Carrot card, is turned over one card at a time. The last carrot card drawn is the Magic Carrot, and its owner is named the winner. A player, however, requires a bunny in play in order to win the game - if a player is without bunnies at this phase, their Carrot cards are given to other players.
Killer Bunnies consists of a 110-card starter deck, as well as Cabbage and Water cards, and 6 twelve-sided dice. Booster sets containing 55 additional cards and other equipment have been released, adding to the complexity of the game. As of the Epsilon revision of the game, Killer Bunnies includes the first booster set. Due to its nature as a noncollectible card game, each expansion relies on gameplay elements found in previous expansions, prompting players to own every previous booster set before acquiring the next one. Some have criticized the piecemeal release, although it is not atypical of collectible card games, in which Killer Bunnies retains a passing resemblance. However, it should be noted that Killer Bunnies and its booster decks were originally designed together, with certain components referencing or referring to mechanics found in later booster decks. There are a total of 10 booster decks:
- The Blue set is the starter deck, and contains eight Carrots.
- The Yellow booster deck adds four additional Carrots to the game, and, as of the Epsilon edition, is included with the Blue starter deck.
- The Red booster deck (2003) adds Red Bunnies, which are bunnies that have built-in abilities that additionally benefit the player. This booster also adds four additional Carrots to the game.
- The Violet booster deck (2003) adds Specialty Bunnies, which are uncolored bunnies which may only be matched with each other to form Bunny Triplets. This booster adds the last four Carrots to the game and the twenty-sided dice.
- The Orange booster deck (2004) adds Pawns to the game, which allow certain dice to be re-rolled when a player has them in its possession, as well as allowing certain cards to be played twice before discarding. You can also make a bunny triplet with a pawn of any color and two bunnies of that same color.
- The Green booster deck (2004) adds Zodiac cards to the game. Players collect Zodiac cards similarly to Carrots, and at the end of the game, but before the Magic Carrot is revealed, one Zodiac card is revealed to be the winning Zodiac symbol, which grants the holder of the respective Zodiac card greater chances of obtaining the Magic Carrot. Half-color bunnies have also been added, where these bunnies may be treated as either of two different colors.
- The Twilight White booster deck (2005) adds The White Stuff, whose holder is granted the exclusive use of a white die which may be substituted for any unfavorable die roll.
- The Stainless Steel booster deck (2005) adds Super Bunnies, which are more powerful but incur additional consequences if they are removed from play.
- The Perfectly Pink booster deck (2006) adds Pink Bunnies, which are similar to Red Bunnies, but are more powerful. It also adds Ranks which may be assigned to bunnies, allowing the player owning the highest-ranked Bunny a special privilege.
- The Wacky Khaki booster deck (2006) adds additional Ranks into the game.
- The Ominous Onyx booster deck (2007) adds Mysterious Places to the game. Players can play Mysterious Place cards, and during the game, the last player to draw one is granted the privilege of deciding the destiny of cards with a yellow ball with a red stripe in the picture. At the end of the game before the Winning Zodiac is revealed, the small Mysterious Place deck is inspected, and the player holding the Mysterious Place which matches the one at the bottom of the deck may take all Zodiacs of one color/type from any opponents.
In addition, "Bunny Blanks" are also available, which allow players to create their own cards. Limited edition "Omega series" cards have also been released, providing a collectible aspect to the game. The "Psi series" cards, included with the Bunny Blanks, are also a second series of collectible Killer Bunnies cards.
In 2004, the kids version of Killer Bunnies, Kinder Bunnies: Their First Adventure, was released. It is a very simplified and largely nonviolent game, created for children as young as 5-years-old. The Sky Blue Starter Deck has very little reading and just a series of basic cards. The Sunshine Yellow Booster Deck (included in the same box as the Starter Deck) requires more reading and may not be suitable for the younger kids. There are no other booster decks available for this game. However the Kinder Bunnies cards can also be added to the Killer Bunnies cards as an eleventh booster deck.
The most common criticism of Killer Bunnies is that the game is ultimately a lottery, with the winner being determined by the random choosing of the Magic Carrot, which is set at the start of the game. Because of this, a player consistently outclassed through the game can still win as long as a single bunny and a single carrot card is retained. Fans of Killer Bunnies contend that this random element keeps the game exciting even when one player's early card draws leave him in a poor position. It also allows less skilled or serious players to enjoy a game against more experienced players. Others have complained about the complexity of Killer Bunnies, especially with the booster packs added to the game.
There are, however, alternate rules that allow for a non-random endgame. Points are assigned for each Carrot that a player has acquired, and the "Magic Carrot" is worth a slightly higher point value. This way, a player with only the Magic Carrot can still be beaten by a player that has dominated the game with collecting many Carrots.
A sequel to the original Killer Bunnies game has been released. Killer Bunnies and the Journey to Jupiter was released in October of 2008. There will be a third game in the series by the name of New Orleans Odyssey, although the name has not been confirmed.