Is there a way to get a Bugdroid challenge whenever I want in Fruit Ninja? Bugdroid provides a 1000 Starfruit reward, so it is an easier way to earn Starfruit than Zen Mode, advertisements, or daily challenges.
I'm pretty sure it's just random.
I haven't been able to make out any pattern in when the challenges happen, and I've also gotten challenged right after opening the app before. Just immediately, before I'd even played a round of anything, which makes me think that you can't trigger the encounter.
If you could, it'd probably be too easy to earn Starfruit. Once you've learned Bugdroid's pattern by heart, there's really no way you will ever lose.