Just a few quick things.
1) You get bodied by Earthquake. Perhaps consider fitting in a defensive flying type such as Lando-T/Celesteela/Zapdos somewhere.
2) Charizard-X isn't in a great spot right now due to an influx of Fairy types, but you also have no way of removing entry hazards. This means Stealth Rocks will destroy him. Rapid spin on Excadrill would help alleviate this. Also Flame Charge seems good in principle, but practically it's near worthless. Either Roost, Will-O-Wisp or Earthquake would be better in this slot.
3) In line with Rapid Spin on Excadrill, drop Sandstorm and change the ability to Mold Breaker. Excadrill isn't threatening enough to have a turn to set up SS, and is hard countered by the most prevalent mon in the tier, Lando-T.
4) Toxapex - Modest nature is useless. Choose a defensive nature that lowers Atk, like Bold. Furthermore, try to choose a defence to specialise in, as that EV spread is far from optimal. Also Baneful Bunker is crap 90% of the time, use Haze instead.
5) Chansey - What does this do other than sit there? No Rocks, Wish support or Heal Bell essentially gives you a Cleric that can't heal. Hardly ideal. Choose a direction you want to go with the previously stated moves. Also with the moveset you have, Protect is nigh useless.
That's just some quick things without entirely redesigning your team. Try using Smogon's sample sets to get a better idea of what to use, in addition they give you useful teammates and other options. It's not perfect, but very helpful when starting out competitive.
