Yes, Guts can be a little brat. ]:
You just have to get real lucky to activate it though.. it's all about prediction.
Like if the opponent sends in Jolteon, you could try and get lucky by throwing in Heracross hoping for a Thunder Wave to hit. XD
I actually use Perish Song Mismagius myself, it almost never fails to succeed in taking one opponent down with it. But honestly, who puts Shadow Ball on a Perish Song Mismagius? The moveset should look like this if you seriously want to succeed;
Mismagius @Leftovers
- Mean Look
- Perish Song
- Protect
- Pain Split
Latios may be faster, but it's in the Uber tier and people can be very stingy when it comes to Ubers.. so you won't see Latios very much in competitive battling.
Therefore, Uxie ftw. (b'u')b
Same with Garchomp, and you'd be stupid to use Garchomp outside of a sand storm team.. so even if Mesprit became a good counter to it, there is still the threat of Sand Veil. XD