Careful Manaphy...
Manaphy @ Leftovers
Careful
Hydration
236 HP / 20 Atk / 252 SpD
~Aqua Ring
~Toxic
~Reflect/ Substitute
~Dive
EV Spread:
It was hard to work with a Careful Nature, so I tried the best I could... assuming it has 31 in hp, 236 hp will give it 400, so leftovers will recover as much hp as possible. 20 atk will help do some decent damage to some, but not all pokemon. Give it max special defense to have a strong special wall.
Moves:
This Manaphy can get really annoying to opponents if used in the correct way. Aquaring and Leftovers will help Manaphy reciver slowly over time. That would be about 1/8 of an HP per turn. Toxic goes pretty well with this guy since he has to stall... Toxic will annoy the opponent combine with Dive. Dive is amazing in adding to the stall power. Aquaring+Leftovers+Toxic+Dive will make the Manaphy really annoying. Aquaring and leftovers will recover health while Toxic will reduce the opponent's HP quickly. And when you dive you make the opponent die faster and you recover alot more. For the last slot you have 2 choices... Substitute or Reflect. Both will add to the annoying stall. Substitute combine with the other 3 moves, can recover all the 25% health lost. Reflect will build up it's defences.
Support:
This guy does not need much support, but you do not want this guy to be affected by status, so Kyogre is a good choice with Manaphy.