Passive wording, replacement effects, and layers

Three things decide what a card's text actually does when it meets other text: which of two conflicting texts wins, whether a replacement effect rewrites the event, and in what order stacked changes apply to a unit. The usual mistake is to treat all three as "the newest card wins". None of them works that way.

When texts conflict. Card text supersedes rules text (rule 002), but it uses its own terminology and is read according to the rules (rule 051). When you cannot carry out everything a card says, do as much as you can and ignore the impossible part (rule 055). If you play Acceptable Losses, "each player kills one of their gear", and your opponent has no gear, you still kill one of yours. When one card forbids what another allows, "Can't beats Can" (rule 054.1). Baron Nashor says he can't be chosen by enemy spells and abilities, so an enemy Blast of Power cannot choose him, however plainly it says "kill a unit". "Only" works the same way (rule 054.2). Only restrictions win like this. Two mandatory requirements that conflict, such as two effects naming different places to play a unit, are not "can't"s, so the player picks one set and ignores the rest (rule 355.17.a). A restriction must still be followed (rule 355.17.b).

Reading passive wording. A passive ability is a statement of fact (rule 364.2), and one containing "if" or "while" is conditional (rule 364.3.a). Disciple of Shen has Shield 3 while it is at a battlefield with exactly one other unit you control. It is not a trigger: at any moment the statement is true or it is not. With two other friendly units there, Disciple has no Shield; once one of them dies, the statement is true again and Disciple has +3 Might as a defender (rule 814.1.c).

Replacement effects. A replacement effect alters how another effect or rule is applied, and is usually marked by "as", "would" or "instead" (rule 368 and rule 369.1). Zhonya's Hourglass reads "If a friendly unit would die, kill this instead. Heal that unit, exhaust it, and recall it." When your unit would die, the Hourglass dies and the unit is healed and goes back to base exhausted; the death never happens, because replacements apply before the event occurs (rule 370.1.c). A replacement applies only once to an event (rule 370.2). "I enter there" and "I enter ready" are replacements too, which is why Baron Nashor still enters at the Baron Pit where a mere permission to play somewhere would lose to an "only" restriction (rule 369.3). If several replacements apply to one event, the controller of the object being acted on picks the order (rule 372). When several events happen at once, each is treated separately, effects with the same controller apply in that player's chosen order, and effects with different controllers execute in turn order (rule 373 and rule 373.1).

Layers. Layers say how effects change the traits and abilities of an object (rule 476), and they apply in a fixed order (rule 479). First Copy Effects (rule 479.1). Second Trait-Altering Effects: name, type, tags, controller, cost, domain and base Might, marked by "becomes", "give", "is" or "are" (rule 479.2.a and rule 479.2.b). Third Ability-Altering Effects (rule 479.3.a). Fourth Arithmetic Effects, which raise and lower Might and costs (rule 479.4.a). Worked example: a unit with printed Might 2 is hit by Eclipse (-4 Might this turn), and later Dragon Form makes its base Might become 5. Dragon Form is a Trait-Altering effect, so it applies before the Arithmetic layer whichever was played first: base 5, then -4, so the unit has 1 Might. Inside the Arithmetic layer increases apply before decreases (rule 479.4.e.1 and rule 479.4.e.2), a limit such as "to a minimum of 1" is fixed when the effect is applied (rule 479.4.b), and you can never increase a number by a negative amount (rule 479.4.c). If one effect in a layer depends on another, apply the one it depends on first (rule 481.2). Otherwise the earlier timestamp goes first (rule 482.3), and a timestamp only orders effects inside one layer.