NFE All-Out Attacker (Marill) @ Eviolite  
Ability: Huge Power  
EVs: 4 HP / 252 Atk / 252 Spe  
Adamant Nature  
- Play Rough  
- Knock Off / Waterfall  
- Ice Punch  
- Aqua Jet  

NFE SpDef Whirlpool Trapper (Marill) @ Eviolite  
Ability: Sap Sipper  
EVs: 248 HP / 8 Def / 252 SpD  
Calm Nature  
IVs: 0 Atk  
- Whirlpool  
- Perish Song
- Protect  
- Rest
Optional Move(s): 
- Belly Drum
Optional Item(s): 
- Choice Band
- Normalium Z
Optional Ability: 
- N/A
Optional EV/IV(s):  
- 172 HP / 252 Atk / 84 Spe (Adamant)
- 248 HP / 120 Def / 140 SpD (Calm)
Overview: Marill can act as both an all-out attacker and a Perish Song trapper. The trapper set has a good defensive typing and Sap Sipper, which means it is capable of tanking enough hits from common Pokemon in the metagame to trap them. However, it suffers from being very predictable and hard to use effectively if the opponent knows what it does or has a Pokemon Marill cannot trap on their team. The all-out attacker set plays off expecting the trapper set and can hit switch-ins hard. However, it is slow and easy to revenge kill.
All-Out Attacker: The all-out attacker Marill set can defensively check and exploit top tier threats like Monferno, physical Sliggoo, and Combusken. Play Rough is a strong STAB attack which hits Dark-, Dragon-, and Fighting-types such as Sliggoo, Machoke, Fraxure, and Krokorok for super effective damage. Knock Off is a fantastic spammable attack which removes Eviolite from bulky walls for teammates and hits bulky Ghost- and Psychic-types like Dusclops and Metang. However, Waterfall can be run over Knock Off if a strong Water-type STAB attack to OHKO Fire- and Ground-types such as Monferno, Combusken, and Krokorok is desired. Ice Punch hits Grass-types such as Roselia and Servine hard on the switch-in. Aqua Jet serves as a useful priority STAB attack.
SpDef Whirlpool Trapper: Whirlpool traps opposing Pokemon for 4-5 turns and accumulates 12.5% chip on them per turn. Perish Song puts a three-turn counter on both Pokemon on the field, meaning that if a Pokemon is still on the field when the counter reaches 0, it faints. Perish Song works well in conjunction with Whirlpool, since it ensures that the opponent cannot switch out to avoid fainting. Protect lets Marill survive a turn without getting damaged, while also reducing the Perish Song counter by 1. Rest gives Marill some longevity and lets it tank hits while asleep. Marill can only guarantee trapping Pokemon which cannot 2HKO it if they switch into Whirlpool and it can only trap Pokemon which cannot 3HKO it if Marill comes in on it on a free switch. It has a 33.3% chance to trap a Pokemon which can 2HKO it if it gets a double Protect. Typically, the optimum series of plays for trapper Marill is Whirlpool then Perish Song then Protect then Protect / Rest then switch. The specially defensive set can trap some standard Clefairy, Kadabra, defensive Roselia, Servine, Mareanie, Sliggoo, Gloom, Prinplup, and Ferroseed sets. It can also trap Pokemon like Eviolite Machoke if it switches into Whirlpool.
Checks and Counters
All-Out Attacker: Mareanie walls Marill; it can easily switch into any attack and force Marill out. Ferroseed can also tank a few hits from Marill and threaten it. Other bulky Grass-types like Servine, Quilladin, and Gloom can easily switch into an Ice Punch and revenge kill or force Marill out. However, none of the above Pokemon appreciate losing their Eviolite. 
SpDef Whirlpool Trapper: Any Pokemon with Volt Switch or U-turn completely neuter the effectiveness of this set, since they can happily switch into Whirlpool, chip Marill on the Perish Song then Volt Switch or U-turn out of the field to avoid fainting to Perish Song. If the Volt Switch or U-turn user has longevity like Staravia or Vibrava, they can continuously switch into and prevent Marill from trapping a Pokemon. Any Pokemon capable of 2HKOing Marill can switch into Whirlpool and avoid being trapped 66.7% of the time. Marill is also extremely pressured by hazards, since hazards allow some of the Pokemon it would trap to be able to 2HKO or 3HKO it.