Page 588 — Ten Times a Decade
As a DM, if you want to hinder the players somehow without being to obvious, you can try "helping" them instead: Tagging along an NPC that has the same aspirations but messes up in some small or big way. Of course, you'll need to previously have had genuinely helpful NPCs tag along so that they don't suspect the plot twist too quickly.
Oh, I'm not implying anything about Spike here, by the way. Sometimes the "helpful" tagalong is just there to poke fun at the players.
Transcript:Applejack: Since I'm in now, I can get my family to help with all the supplies we need. That should help speed things along.
Twilight Sparkle: I guess we should figure out our roles, then. I'd make a pretty impartial judge, since you're both my friends.
Fluttershy: I'm sure some of my animal friends wouldn't mind volunteering as staff.
Pinkie Pie: I can spread the word and make this event the talk of the town!
Rarity: I can… help decorate.
Spike: And I can be the announcer! "Hello, everyone, and welcome to the First Annual Iron Pony Competition!"
Twilight Sparkle: We're doing this again next year?
Spike: "Annual" just makes it sound more official. C'mon, Twi, this is basic stuff.