It would be a 7/2. Power/Toughness switching is the last sublayer to apply in layer 7. So first dive down's effect applies making the Crag a 2/7 (layer 7c), then the P/T switching (layer 7e) applies afterwords which makes the Crag a 7/2.
It's a 7/2. Power and toughness switching occurs in the very last layer, 7e, so you apply all other changes to power and toughness before you switch.
613.3e Layer 7e: Effects that switch a creature’s power and toughness are applied. Such effects take the value of power and apply it to the creature’s toughness, and take the value of toughness and apply it to the creature’s power.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Its new power and toughness is 4/1. A new effect gives the creature +5/+0. Its “unswitched” power and toughness would be 6/4, so its actual power and toughness is 4/6.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Its new power and toughness is 4/1. If the +0/+1 effect ends before the switch effect ends, the creature becomes 3/1.
Example: A 1/3 creature is given +0/+1 by an effect. Then another effect switches the creature’s power and toughness. Then another effect switches its power and toughness again. The two switches essentially cancel each other, and the creature becomes 1/4.
613.1g. Layer 7: Power- and/or toughness-changing effects are applied.
(...)
613.3. Within layer 7, apply effects in a series of sublayers in the order described below. Within each sublayer, apply effects in timestamp order. (See rule 613.6.) Note that dependency may alter the order in which effects are applied within a sublayer. (See rule 613.7.)
613.3a. Layer 7a: Effects from characteristic-defining abilities that define power and/or toughness are applied. See rule 604.3.
613.3b. Layer 7b: Effects that set power and/or toughness to a specific number or value are applied. Effects that refer to the base power and/or toughness of a creature apply in this layer.
613.3c. Layer 7c: Effects that modify power and/or toughness (but don't set power and/or toughness to a specific number or value) are applied.
613.3d. Layer 7d: Power and/or toughness changes from counters are applied. See rule 121, "Counters."
613.3e. Layer 7e: Effects that switch a creature's power and toughness are applied. Such effects take the value of power and apply it to the creature's toughness, and take the value of toughness and apply it to the creature's power.
+X/+Y effects and "switch" effects are applied on different sublayers, so the order their started existing (their timestamp) doesn't matter. Switching is the last sublayer, so you basically calculate a creature's Power and Toughness normally, with all the pluses and minuses applying to the Power or Toughness as normal, and only then you switch the two numbers.
Puca starts as a 2/4, gets +0/+3 on sublayer 7c to be 2/7, and then switches to 7/2 at sublayer 7e.
And if activate Puca's ability first, let it resolve, and then cast Dive Down, Puca will also end up a 7/2.
Continous effects that change the characteristics of objects are applied in a series of layers. To determine an object's characteristics, you go through the layers in the predescribed order. Only within a layer do the time stamps of the effects matter. Power/toughness modifying happens in layer 7c, while power/toughness switching is done in layer 7e (the very last layer, so switching always happens last). This means, that your Crag Puca is a 7/2, regardless of the order the two effects have been created in.
613.3e. Layer 7e: Effects that switch a creature's power and toughness are applied. Such effects take the value of power and apply it to the creature's toughness, and take the value of toughness and apply it to the creature's power.
And if activate Puca's ability first, let it resolve, and then cast Dive Down, Puca will also end up a 7/2.
The second sentence of 613.3e just explains, how the switch is done. The reason why the order in which the effects are created doesn't matter for the end result in this scenario, is that power/toughness modifying is always calculated before the switch due to it happening in an earlier layer. When applying an effect, you take into account all effects that have already been applied before it. So you do the switch with the modified power/toughness.
Dive Down resolves.
I activate Crag Puca's ability.
Is Crag Puca 7/2 or 4/5 until end of turn and why?
(...)
613.3. Within layer 7, apply effects in a series of sublayers in the order described below. Within each sublayer, apply effects in timestamp order. (See rule 613.6.) Note that dependency may alter the order in which effects are applied within a sublayer. (See rule 613.7.)
613.3a. Layer 7a: Effects from characteristic-defining abilities that define power and/or toughness are applied. See rule 604.3.
613.3b. Layer 7b: Effects that set power and/or toughness to a specific number or value are applied. Effects that refer to the base power and/or toughness of a creature apply in this layer.
613.3c. Layer 7c: Effects that modify power and/or toughness (but don't set power and/or toughness to a specific number or value) are applied.
613.3d. Layer 7d: Power and/or toughness changes from counters are applied. See rule 121, "Counters."
613.3e. Layer 7e: Effects that switch a creature's power and toughness are applied. Such effects take the value of power and apply it to the creature's toughness, and take the value of toughness and apply it to the creature's power.
+X/+Y effects and "switch" effects are applied on different sublayers, so the order their started existing (their timestamp) doesn't matter. Switching is the last sublayer, so you basically calculate a creature's Power and Toughness normally, with all the pluses and minuses applying to the Power or Toughness as normal, and only then you switch the two numbers.
Puca starts as a 2/4, gets +0/+3 on sublayer 7c to be 2/7, and then switches to 7/2 at sublayer 7e.
And if activate Puca's ability first, let it resolve, and then cast Dive Down, Puca will also end up a 7/2.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
Because of the second part of 613.3e?
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)