Se Jun's pachirisu was an extremely niche case. It's niche is that it can redirect flying and electric attacks and paralyze things even when taunted. In 2014, with Talonflame and Rotom everywhere, this was extremely handy. However, things are far more powerful in 2015. Landorus-T, which completely destroys Pachirisu, is absolutely everywhere. It also faces increased competition as a follow me/rage powder user from Togekiss, which can also paralyze things, is bulkier, can spam Serene Grace air slashes and has tailwind. It also faces competition from Clefable and Volcarona, and still has to beat out Lucario and Amoonguss for the spot. Additionally, Thundurus is the far better electric type support Pokemon as it is immune to Earthquake, has taunt and has pranskter. The main reason Pachirisu was so effective was not that it was particularly good but because it had surprise value, and that surprise value is now lost.
Quite simply, Pachirisu is only worth it if you play to its strengths in every way possible. Se Jun Park's team had both Gyarados and Talonflame, which both appreciated electric redirection, and Scarf Gardevoir, which appreciated redirected Brave Birds and Bullet Punches. It had Shadow Tag support from Gothitelle to give Pachi favorable matchups. Pachi did very little work itself. but immensely supported it's destructive team mates. Pair pachi with powerful sweepers weak to steel, electric or flying, and also have multiple counters to landorus-t and garchomp on your team. Gyarados is a solid partnerthat I think is almost essential. Other potentially good partners can include Breloom, Bisharp, and many other slow powerful attackers.
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