I think if they stated VS Blizzard or something it would make more sense. Even VS not Focus Blast might work, Earthquake is relatively weak, lacks STAB, and is coming off a legendary with the lowest attack we've seen since Suicune so a high-enough leveled Tyranitar could shake it off. Focus Blast is a one hit kill move and Tyranitar should be kept on the sidelines for it.
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Issue with Tyranitar against Regice
It wouldn’t work as a counter against it event with partly cloudy weather right? Since Regice could carry RS, FB and Earthquake, I want to think it would worth against Frosth Breath/ Blizzard only
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SD Ttar has the highest time to win when it's partly cloudy, against any moveset, on Pokebattler. If you get fight moves, well, he'll go down fast, but do a lot of damage before going down. He's a lot easier than Kyogre, that's for sure.
I did a focus blast one today, and each Ttar got off one stone edge. They are levels 35 and 33, with SD/SE.