Game Rules

Shuffle the deck and deal hands according to the number of players. (See RULES: 1.a)
Place the remaining cards face down in a spot accessible to all players. This becomes the deck, known as the Stockpile, that cards are drawn from.
Randomly decide which player goes first. (See RULES: 1.b)
Using a marker (coin, bottle cap, trinket), designate the center space of the playing area. The playing area is a 5 X 5 grid of spaces, called the Core, where players can place cards. (See RULES: 1.c)
A MAD playmat is recommended for ease of visualization and picking up.
The last part of the setup is a seed card phase called Nuclear Proliferation (NP). Starting with the first player, and passing to the left, each player will take one turn placing a card from their hand on any space on the Core that is not adjacent to (does not share a side with) another placed card. (See RULES: 2.a-b)

After NP, Nuclear Escalation (NE) begins, and is active for the rest of the game.
Each player must place one card on each of their turns, and only in spaces that do share a side with (are adjacent to) at least one other previously placed card.
The newly placed card must share either a number or an element (color) with at least one adjacent card. (See RULES: 2.c)
If a player does not have a legal move, they must draw from the Stockpile until they receive a card that is a legal move, then place it. (See RULES: 2.c.iii-v)
If a player placing a card results in one or more Criticalities being created, that player must pick up all cards in the Criticality(ies), then every other player experiences Fallout and must draw a card from the Stockpile. (See RULES: 3.a-b)
The winner of the game is the player with the fewest cards in their hand at the end of the game.
The game ends when one (or more) of four conditions are met; the last card is picked up from the playing area (other players still draw a card, if possible), the last space on the playing area is filled (as long as no Criticalities are created), a player places the last card from their hand (as long as no Criticalities are created), or one or more players go to draw a card and there are none/not enough left in the Stockpile. (See RULES: 4.a-c)

The goal of the game is to have the least cards in hand at the end of the game.
One can achieve this by strategically placing cards and picking up cards such that one has more options in their hand and their opponent has fewer.
Picking up cards is part of the game. A good player knows when to do it, and what cards are valuable based on the Core state and other players’ hands. (Pro tip: you can place cards to create Criticalities and pick up even if you have a move that doesn’t require a pick-up)
The geometry and arrangement of cards on the Core is important in forming a plan. A good player knows where and when to place cards that allow their future moves while denying other players’ moves. A really good player can read the intention of future moves based on where another player decides to place a card. (Are they denying plays or promoting?)
Feel free to play dirty, but importantly, have fun. Remember, friends are temporary, but Mutually Assured Destruction is forever

Deciding first player: The first player is selected randomly.
Playing area (Core): The playing area is a 5 X 5 grid of spaces.
Each space may be placed on, when legal to place a card there.
A MAD playmat is recommended for ease of visualization and card placement/removal.

The Stockpile consists of cards numbered 1 through 13.
There are 13 cards in each element.
There are 4 elements in the game; Plutonium (Pu, purple), Radium (Ra, red), Thorium (Th, light blue), and Uranium (U, yellowish-green).

The number of cards in any player’s hand must be disclosed, if asked for.
The number of cards in the Stockpile may be counted.
Cards that were most recently picked up from the Core must be shown if picked up hastily. After another pick-up occurs, they do not need to be disclosed.

Pass turns to the left hand side.
A player’s turn starts when the player to their right is no longer physically touching the card they placed or when the cards they picked up are no longer touching the playing surface and every other player has drawn their card.
Every player must place exactly one card on the Core on each of their turns.
Players may only place cards during their turn.

NP consists of each players’ first turn of the game.
During this phase, a player must place any card from their hand anywhere on the Core that does not result in two or more cards sharing a side with another card. i.e. During NP, adjacent spaces on the Core must not be occupied simultaneously.
After the last player in the turn rotation places their first card of the game, the SCP ends and normal card placement rules begin.

After NP, NE rules are active for the rest of the game.
During NE, cards must only be placed in spaces that are adjacent to cards on the Core.
A legal move consists of a card being placed such that it shares a side with one or more cards of the same number and/or element.
If a placed card results in one or more Criticalities being created, the player who placed that card must pick up that card and all other cards in the Criticality(ies).
If the active player does not have a legal move in their hand, they must draw one card from the Stockpile at a time until a legal move is drawn. Then, that card must be placed, even if it results in one or more Criticalities being created.

A Criticality is created when a card is placed, if that card creates a group of cards, totaling 3 or more cards, that all share a side with each other, and those cards are all of the same number or element. Example: Consider if a player places a Thorium (blue) 8 on the space marked with an X. The second image shows one of two Criticalities created, and the last image shows the second Criticality created.
Criticalities are constituted of three or more placed cards on the Core. Two placed cards that share a side as well as a number or element are not considered Criticalities, but another card placed on any adjacent space of these two cards would create a Criticality.
There does not need to be two adjacent cards of the same type on the Core for a placed card to create a Criticality. A placed card can be “sandwiched” between two adjacent cards and still create a Criticality.
A placed card can create more than one Criticality.
Criticalities can overlap with each other upon creation.

Whenever a placed card causes one or more Criticalities to be created, the player that placed that card picks up all cards in all created Criticalities, puts them into their hand, and their turn is over.
Fallout happens whenever one or more Criticalities are picked up during a turn.
Each other player must simultaneously draw one card, as long as there are enough cards in the Stockpile.
If there are not enough in the Stockpile, no one draws a card and the game ends when the cards from the Criticality(ies) are picked up