Naganadel is a glass cannon set-up sweeper that is really straight forward to use. In fact, its moveset is so reliable and effective that most teams come prepared for it, so you'll have to set up quickly and outplay your opponent.
It also has poor defenses, so it can't easily set up. Here's a good way (with moveset) to make the most of it.
Naganadel @ Dragonium Z
Ability: Beast Boost
EVs: 252 SpA / 4 SpD / 252 Spe
- Draco Meteor
- Sludge Wave
- Nasty Plot
- Fire Blast
(This is the standard Smogon set)
Bring it in against defensive Pokemon (Chansey or Toxapex, for example) when you think they will use Toxic, or some move that won't damage you. Then, use Nasty Plot (if the opponent doesn't have a faster Pokemon on their team). If you suspect a Scarfed Pokemon in the team, use an attack. However, if there are no potential Scarfs or faster Pokemon, use Nasty Plot and begin.
Use Devastating Drake for exceptionally bulky switch ins, or for the first kill. This is will activate its Beast Boost, which, due to Timid Nature, raises Speed and in turn makes it so much easier to sweep.