For TZ, I thought about trying to get something like 3 dead ends, because that's an odd shot that most people don't go for. Could also do collect 10 hitchhikers or something, but you'd need to turn on tournament mode to make it more fair.
With Mystery Spot, I figured that with 5 balls, it'd be much easier to get, and would be something you could concentrate on rather than just happening onto it. It also makes things tricker, since I find the "light otto" easy to drain off of.