Taking back decisions, shortcuts and angle shooting

Players are responsible for considering their options before they act, and an action that has been communicated to an opponent can't generally be taken back (TR 509.1 and TR 509.2). The exceptions are narrow, they depend on the event's OPL (Organized Play Level), and they are the single most common reason a judge is called to a close game, so they are worth knowing precisely.

At low OPL a player can reverse their most recent action and decide differently, including not acting at all, as long as neither player has taken a new action since. The change does not have to be immediate (TR 509.3). At high OPL the same idea applies only in three situations, and it must still be the case that nobody has taken a new action: right after all the choices for putting a spell or ability on the chain have been communicated, right after playing a unit or gear to a location, and right after a choice such as moving a unit with a Standard Move (rule 144.4.a) or discarding a card (TR 509.4, TR 509.4.a, TR 509.4.b and TR 509.4.c). At every OPL you can always ready runes you just exhausted for Energy (rule 164.2.a), or unrecycle runes you just recycled for Power, if no new action has been taken and Focus has not passed, including when you change a decision (TR 509.5 and TR 509.5.a).

The limits matter as much as the permission. At high OPL this flexibility is not a tool to reverse a decision once an opponent has been required to indicate information that shows the decision to be a tactical error, for example after you commit to an attack and the opponent says their unit is bigger than you thought (TR 509.6). A decision made from public information that was represented inaccurately can still be rewound at the head judge's discretion, but misrepresenting information to get a rewind is cheating (TR 509.6.b). And you may not change a decision in response to an opponent's physical reaction or because they have started a game action. Doing so to gain information is angle shooting, which is a Warning (TR 509.7 and TR 704.4). Taking back decisions does not excuse slow play (TR 509.8).

Shortcuts are the other half of the topic. Players may skip parts of the technically precise sequence without announcing it, usually by skipping steps to everyone's shared understanding, and a new shortcut must come with a clear statement of the game state at its start and end (TR 503.1, TR 503.2 and TR 503.3). A shortcut can be interrupted by saying where you want to act, but not with the intent to do nothing, and you can't use an unannounced shortcut or change one without saying so (TR 503.4, TR 503.6 and TR 503.7). When resolving something, you can't assume your opponent is using a shortcut without asking (TR 503.8). Four are common. Channeling or drawing at the start of a turn means you have passed through the Beginning Phase. Putting something on the chain means you are passing priority unless you say you are retaining it. Announcing a choice that is normally made on resolution commits you to it unless opponents react. And asking about such a choice means you are passing priority and letting the item resolve (TR 503.9.a, TR 503.9.b, TR 503.9.c and TR 503.9.d). Asking an opponent to state a choice they would make on resolution before you decide whether to react is itself angle shooting (TR 704.4.a.1). A shortcut also may not reorder actions to give you information early, and a recycled card must go on the bottom of the deck immediately (TR 504.3 and TR 504.4).