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When I read this request I was in front of a wild pidgy in SS whilst trying to catch some apricorn ball pokemon. It is now in a fast ball. Unfortunately, I won't get it across to GEN 6 until tomorrow.
I also have a Safari ball Tyranitar. I can breed the Female larvitar for you. PM if you are...
To get HP Ice with 31 in SpA, Spd, and Sp you need to have even defense and at least 1 of HP and Attack to be even
To calculate chance of this we look at the different places the 3 guaranteed 31s can be.
If 3 possible guaranteed 31s SpA SpD Sp, a 1/20 chance, HP Ice is 3/8
If 3 possible...
Firstly, I did mean NightShade on turn 3 (I will edit it to make sure anyone who reads from now on doesn't get confused).
Second, I haven't actually SR'd Thunderus yet, I have been havong far too much fun working out theoretical means to SR things efficiently.
That Stats I figured for to SR a...
With Thunderus I think you are better to start with a Prankster Sableye with pain split, taunt and night shade. Turn 1 use pain split. This will give you your HP check, and if Thunderus uses agility or Heal Block you have your speed check. If on the other hand Tornadus uses Crunch or Discharge...
Try giving smeargle Leftovers instead of Focus Sash, with Z being asleep most of the time, it should hopefully keep Smeargle alive. If this isn't enough try a Smeargle with 31 speed IV as this will allow more EV in defense.
If that still isn't enough you could go for a Jolly Level 100 Amoongus...