The fairy tournament will be loaded with Mega Mawile, so pack your own Klefki and Mawile to make up for the steel weakness, and if you bring Wigglytuff and/or Slurpuff, load up on Flamethrower or Fire Blast. With a particular build, you can outspeed most Mawile with Wiggly and OHKO them with your fire, especially after getting a SpecAtk boost from Competitive.
I haven't seen many hipowdons with stockpile lately xD I usually see them as an annoyance with sr and eq, so I wouldn't fear. Not many people run hippowdons anymore really
But every poke has its weaknesses. Like messing around with aegislash vs sableye. That thing can hard counter aegislash so hard. after you burn it, and taunt it, its over
Stuff like that just makes me think that the game is pretty much balanced
My Lead Hippowdon is a careful stockpile set with max special defense and defense, slack off, crunch and earthquake, holding a weakness policy. It wrecks s**t hard if the opponent can't burn or toxic it, or set up with something that can both wall it and is able to boost it's own stats/ take advantage if it's weaknesses, like Scrafty, Ferrothorn or vaporeon, or something that hits hard with stab special water, ice or grass attacks and can outspeed it, like greninja or Froslass.
I can usually take out 3-4 of my opponent's pokemon with it before they finally take down her down if they dont lead with a counter. My team also runs pok'e mon to counter the counter's though, such as Stockpile Cradily or Gastrodon with recover and leftovers with storm drain, or for stallers, stall breakers like eviolite gligar with immunity and knock off.