Though Dragalge is a Water-type and Poison-type, the best moves that players can use are Dragon-type attacks. It's a lot like Gyrados in that sense; a Dragon in every way aside from base typing within Pokemon GO.
In Pokemon GO, there are typically defensive and offensive movesets. Defense is based on defending a gym against PvE Pokemon. The offense is best used for PvP battles or anything else by default. In the case of Dragalge, both offensive and defensive movesets are the same.
For the fast attack on Dragalge, players should use Dragon Tail. It does by far the most damage when compared to the other fast attack options. The energy per second gained from Dragon Tail isn't as high as the others like Water Gun, but it isn't far off.
When choosing the Dragalge charge attack, players should use Outrage. Outrage has Dragon-typing, and it charges just as faster as anything else with more damage than Aqua Tail. If players decide to use a second charge attack, then Gunk Shot is a fantastic choice. It's slow to charge, but it has Poison-typing and a ton of damage.
How to get Dragalge in Pokemon GO
In order to get a Dragalge, players need to encounter a Skrelp a handful of times. Skrelp and Clauncher both made their debut during the Pokemon GO Rivals' Week.
Players need a total of 50 Skrelp candies to evolve one into a Dragalge. Skrelp itself can be found in the wild, or in one-star raids during events such as the Rivals one which just ended. It takes about 16 encounters without any berries or transfers to get a Dragalge in Pokemon GO.