You are right, I should not be allowed to post on 4 hours of sleep. Apologies friend.
...Actually wait a minute. If I'm not mistaken, trick/switcheroo-ing a Choice item doesn't have an ex post facto effect, unlike Encore. Wouldn't it lock the user into the move they choose that turn? Or can someone confirm this for me?
It locks the move I would use next turn ya.
If you go with Switcheroo
+1 4 SpA Choice Specs Pixilate Sylveon Hyper Voice vs. 4 HP / 0 SpD Delphox: 153-181 (52.3 - 61.9%) -- guaranteed 2HKO
252 SpA Delphox Fire Blast vs. 252 HP / 252+ SpD Sylveon: 99-117 (25.1 - 29.6%) -- guaranteed 4HKO
If you don't
252 SpA Choice Specs Delphox Fire Blast vs. 252 HP / 252+ SpD Sylveon: 147-174 (37.3 - 44.1%) -- 100% chance to 3HKO after Leftovers recovery
+1 4 SpA Pixilate Sylveon Hyper Voice vs. 4 HP / 0 SpD Delphox: 102-121 (34.9 - 41.4%) -- guaranteed 3HKO
So Delphox still wins cuz outspeed if you don't go use Switcheroo and I CM on the switch. +0 Hyper Voice is a 4HKO.
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Greninja @ Life Orb
Protean
Timid
EVs: 4 HP / 252 SpA / 252 SpD
- Hydro Pump
- Dark Pulse
- Ice Beam
- Grass Knot
252 SpA Choice Specs Delphox Grass Knot (60 BP) vs. 4 HP / 0 SpD Greninja: 238-280 (83.2 - 97.9%) -- guaranteed 2HKO