Under Trick Room, Azurill can take advantage of its enormous 24 Attack stat. Return is its primary STAB option, possessing enough power to knock out a huge portion of the metagame in one or two hits. Double-Edge can also be used for the boost in power, yet the recoil ensures Azurill will fall to nearly any reasonably strong priority move. Waterfall is used as a coverage option, allowing Azurill to hit Pokemon such as Duskull or Gastly for neutral damage. Encore allows Azurill to catch Pokemon such as Ferroseed, which might try to set up on it, giving Azurill either a free attack or a free switch. Toxic can be used as well in the third slot to cripple Frillish, which otherwise walls Azurill entirely. Substitute works to take advantage of the free turn offered by Encore, as most Pokemon cannot take two hits from Azurill and live to tell the tale. Because using up Trick Room turns on non-attacking moves can be largely a waste, Azurill may be better off just spamming attacks rather than predicting switches to use moves such as Toxic or Encore. Using Hidden Power Fire over either Encore or Toxic is a viable option, as it can ensure a 2HKO on Ferroseed if Azurill is behind a substitute.
The EV spread for this set seeks to take advantage of the free EVs Azurill has access to, thanks to the fact it needs no investment in Speed. A Brave nature, in conjunction with the lack of investment in Speed, ensures Azurill will be outspeeding nearly every other Pokemon in Little Cup, even Slowpoke and Ferroseed. The rest of the EVs are put into Azurill's defenses, as without any investment, Azurill will go down to priority far too quickly.
Two of the major counters to Azurill are Ferroseed and Frillish, as they resist Azurill's entire movepool and can set up for free on it. For this reason, running Misdreavus alongside Azurill is a good option, as it can reliably take out both of those threats with relative ease. Also, in order to function at all, Azurill must be run alongside a Pokemon capable of setting up Trick Room, such as Slowpoke or Bronzor. Another support option is Rain Dance, which can be set up by both Slowpoke and Bronzor as well. Under Rain Dance, Azurill becomes an even more fearsome foe with its boosted Waterfall, and can only reliably be walled by Pokemon with Water-type immunities, such as Frillish, which can be crippled by Toxic or used to set up on by Vullaby. Packing a Pokemon capable of setting up entry hazards is also very important when using Azurill, as the added residual damage from a few layers of Spikes or Stealth Rock can be vital in achieving key KOs. For this reason, Ferroseed, and Dwebble all make great teammates for Azurill. Also, Knock Off Tentacool can be a great partner for Azurill, as very little can take repeated hits from Azurill without Eviolite.