The Switch Always Comes Last
Corner Cases+3/+0 on the switched creature — and the 3 ends up on toughness.
Cards involved
The switch
Your opponent casts Twisted Image on your Omenspeaker (1/3): power and toughness are switched until end of turn.
613.4dLayer 7d: 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.
Now a 3/1
Twisted Image resolves: the Omenspeaker is a 3/1. So far, so intuitive.
613.4dLayer 7d: 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.
What happens?
You pump AFTER the switch.
You cast Sure Strike (+3/+0) on the switched Omenspeaker. What is it now?
Pick an answer to continue.
The switch has no "point in time" in the result — it sits firmly in 7d, after all setting (7b) and modifying (7c) effects (613.4d). Your +3/+0 is applied BEFORE the switch and ends up on toughness after it. The official CR example calculates exactly this way.
613.4dLayer 7d: 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.
613.4cLayer 7c: Effects and counters that modify power and/or toughness (but don’t set power and/or toughness to a specific number or value) are applied.
Rule of thumb
For switched creatures, apply every further change to the UNSWITCHED values first, THEN flip. And: two switches cancel out. Explaining this calmly at the table means you've understood the L3 heart of the layer system.
613.4dLayer 7d: 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.
Stack
Omenspeaker
Your 1/3 creature
Twisted Image
Switch power and toughness
Sure Strike
+3/+0 and first strike until end of turn
The stack is empty.
Battlefield
—