478.1. Layers are applied and evaluated continuously. All Game Objects have their layers updated in the same instant, but each Game Object is treated separately and individually when evaluating layers.
478.1.a. If evaluating a Game Effect's applicability depends on information from one or more other Game Objects, that Game Effect has an object level Dependency. Pause evaluating the layers of the dependent Game Object and evaluate the layer effects of those Game Objects whose information is referenced. Continue once the applicability of that Game Effect has been established or disqualified. Example: A 4 [M] unit reads in part "While I'm [Mighty], I'm a Yeti." Another unit reads in part "I have all tags of units you control." When the 4 [M] unit is buffed, the layers for all game objects are evaluated. While evaluating the layers for the second unit, it requires us to pause and evaluate the layers for all other units. When we're evaluating the layers for the 4 [M] unit, after all is said and done, the unit has the Yeti tag. Once we've evaluated all units, we go back to evaluating the second unit, and at that time it has the Yeti tag as well.
478.1.b. If a Game Object has an object level dependency with a Game Object that itself has an object level dependency with a third Game Object and so on, determine the final point of the dependency chain and evaluate the layer effects of that Game Object first, continuing up the dependency chain until all Game Objects have had their layer effects evaluated.
478.1.c. If a dependency chain loops back around on itself, identify the minimum set of Game Objects in the loop and evaluate their layer effects simultaneously, layer by layer. If any of them have Game Effects that reference Game Objects from outside the set, pause and evaluate those Game Objects first before continuing with the set. Example: A 4 [M] unit reads "If there is a [Mighty] enemy unit here, I have +5 [M]." Both players control one of these units at a battlefield during combat. Each one is buffed. A third player plays Siphon Power, which reads "Choose a battlefield. Give friendly units there +1 [M] this turn, and enemy units there -1 [M] this turn, to a minimum of 1 [M]." Both of the units there are given -1 [M]. Because they have effects that reference each other, they have a dependency chain. After evaluating their layers simultaneously, layer by layer, both units will be 4 [M].