I think you have done a lot of good work with this team already. You've got some good synergy, as well as some good overall team structure and resistances. I definitely like Terrakion, Thundurus-t, Starmie, and Mamoswine. Ferrothorn seems like it's your dedicated Rain resist and Hazard setter; however, it really strikes me as dead weight. It slows down your offensive pace, and a lot of teams have Pokemon dedicated to punishing Ferrothorn. In addition, Chandelure is definitely out of place. The main reason to use Chandelure would be to Spin Block, but you don't have any Spikes to protect. I think you could get a lot more utility out of that slot. I'll focus on switching Ferrothorn and Chandelure to help improve your team synergy and overall goal.
First, as I mentioned earlier, Ferrothorn doesn't fit on your team. I'm going to recommend that you try Sub DD Gyarados in that slot. Gyarados is a hugely underrated threat, and it would fit perfectly on your team. Mamoswine and Terrakion lure Bullet Punches for you to set-up. Starmie support Gyarados with Rapid Spin support. Those perks aside, the big selling point is Thundurus-t + Gyarados. It's pretty difficult to revenge kill Gyarados without using an Electric move, and that's where Thundurus-t comes in. Get those free Volt Absorbs, and potentially a free Agility / Thunder. One of Thundurus-t's biggest problems, Hippowdon, is also free set up for Gyarados. In addition its great synergy, Gyarados will be a great weapon against opposing Rain Teams. In this metagame, you can never be too prepared for Rain teams. Between Gyarados, Thundurus-t, and Starmie, you'll have Rain teams struggling to keep up.
Next, I'm going to recommend Choice Band Scizor instead of Chandelure. Your team is pretty fast paced and offensive, and I think you could use a little defensive backbone. Scizor is the perfect Pokemon to fill that role. Steel is the premier defensive type, it hits incredibly hard, and it can trap some annoying threats for your team. For example, Lati@s looks close to unmanageable right now, but with Scizor, you can open holes for Thundurus-t to tear through the opposing team. Scizor will help you keep up your offensive momentum, and when the situation demands it, Scizor can revenge many threats. Mamoswine and Terrakion won't be able to do it all, and having more options makes it harder for your opponent to predict correctly.
Besides those two major changes, I have some small ones for you. You might want to try Offensive Life Orb Rapid Spin Starmie. If you rely on Starmie as your main pivot, I'd probably keep it Defensive though. If you stay with Defensive, use Psyshock. It has more general utility in the metagame even though Psychic is stronger.
Put Stealth Rock on Mamoswine. I removed Ferrothorn which was your Stealth Rock user, so you should fit Stealth Rock somewhere on your team. Superpower is pretty useless in my experience, only hitting Ferrothorn and maybe Rotom-w. You should be Revenge Killing with Ice Shard or hitting hard with Earthquake and Icicle Spear most of the time anyway.