I happen to love this prickly little guy, and even though they don't have much to work with, I came up with two movesets that I think have some potential!
Maractus @ Sitrus Berry
EVs: 252 HP, 252 Atk, 4 Def
• Cotton Guard
• Seed Bomb
• Drain Punch
• Knock Off
You aren't get anywhere with Special Defense, so being physically tanky with good HP and Defense is the way to go. Cotton Guard drastically buffs Maractus's defense and since it only takes two turns to max out your defense, having to switch out against a special attacker while you are fully set up isn't so taxing. Knock Off will get rid of your opponents items and Drain Punch will provide consistent sustain, stacking well with Water Absorb and Maractus's Sitrus Berry. Finally, having a strong STAB attack is the perfect way to round out this moveset.
Maractus @ Leftovers
EVs: 252 HP, 252 Sp. Atk, 4 Def
• Spiky Shield
• Cotton Guard
• Giga Drain
Cotton Guard returns for this moveset and pairs well with Spiky Shield, which will punish contacting physical attackers (and Draining Kiss, most likely from a Triage Comfey) who dare to try and get through your defenses. Maractus gives up Water Absorb for Storm Drain, boosting it's Special Attack and the new healing option of Giga Drain (along with Leftovers) hit even harder! Since Maractus has such a shallow Special movepool, I'd recommend filling it's last moveslot with a status move like Toxic or Accupressure. Toxic would be useful for wearing down Pokémon who resist Giga Drain or are very bulky, while also pairing nicely with Spiky Shield. Accupressure adds a little random zest to your battle, buffing one random stay for you or your ally in Doubles. If you are running this Maractus in Doubles, I'd recommend running it next to a wall (or just Specially tanky) Pokémon with Surf for Storm Drain. You could also have it run Toxic and Protect to help stall. I recommend Mantine, which could run Roost as it's last move.
These two Maractus make good use of their Abilities and limited movepool. Even though they aren't the strongest Pokémon out there, they could definitely catch your opponent off guard!