Am I considered Top userish being in the top 10?
Either Way I feel I can answer this with a few things I've noticed.
So I'll just do an overview of everyone.
Ferrothorn - Perfect, I honestly Couldn't say anything to improve here, the Ev's were amazing.
Hydreigon - Also looks Good, Even though I think a Strong Hidden Power might would be better than U-turn, its really an Opinion.
Terrakion - Oh no, We've found a Problem.
Okay, You already have a Fighting Type Tank, and this Guy is your Second Scarfed Pokemon, and Really doesn't play too great of a Role in your Team.
Scarfed Close combat, Can be switched into a pokemon like Chandelure and Calm Minded,
Earthquake is easily countered with all of the Levitating Pokemon, So really, when using him, its quite easy to get yourself into a Mess real Quick.
I Strongly Reccomend Excadrill in his Place,
Now I'm not normally one to Suggest a filler into someones team, but with Volcarona on your Team, you have some serious Problems with Stealth Rock, So you could get a Rapid Spin or Sweep or Both Excadrill to come in and Balance things out here.
Conkeldurr - Okay, I was a bit confused here, I see Guts, yet I see No Flame Orb.
Leftovers is pretty nice to get Gradual Recovery, and I see that you are depending on being able to get a Status Ailment And get Guts Activated, but that most likely won't happen Easily.
Jellicent - I like the Creativity on the set, and Overall love him, Great member of the team.
Volcorona - Leftovers is Cool, But After adding Spinning Excadrill, Life orb Might be a Possible Choice, just something to think on.
So Overall, I think The team is Great As usual, I think I cleared my main problems up already, and I wish you the best of luck in the tournament. :D