This is a set I have particularly enjoyed using.
Jirachi @ Choice Scarf
Trait: Serene Grace
Nature: Jolly
EVs: 252 Attack / 252 Speed / 6 HP
- Trick
- Magic Coat
- U-turn
- Iron Head
This Jirachi is pretty much the perfect counter to Deoxys-D. Fortunately, Mental herb and magic coat do not prevent trick, so with this Rachi in the lead position, there are a number of things you can do. If you're facing a Deoxys-D, then you can just trick it a scarf, and watch as the momentum switches to your side of the field. If they decide to only get up rocks, then you can u-turn out to whatever they switch out to, and proceed to have the game be in your favor. If they magic coat and you trick them a scarf, then they can either A. Go for rocks. B. Set up spikes. Or C. Switch out. Now, with Magic coat, 2 out of those three options will spell doom for them. After they see you're running magic coat and deflect their hazards back at them, then you can just u-turn out on the obvious switch, and then it's actually YOU making all the moves of the game. Deoxys-D's only offensive option to hit Jirachi is fire gem boosted HP Fire, which it can't even use since you trick it the scarf. This Rachi also helps out late game, being able to trick an item you got earlier onto something that doesn't appreciate it. Say you tricked a chansey your scarf, now you have an eviolite to trick onto something else. If you choose to keep your scarf intact, then you are able to keep up offensive pressure with scarf u-turn. If you lead with this rachi and it's an unfavorable matchup, then you can just u-turn out and have rachi serve as a way to cripple walls, and as a way to bounce back the opposing hazards.