Cresselia is a great Mixed Wall.
Cresselia @ Leftovers
Ability: Levitate
Nature: Bold
252 HP/252 Def/4 SpD
-Moonlight
-HP Fire/Psychic
-Ice Beam/Reflect
-Thunder Wave/Toxic
Despite wishing that it just had a little bit more to work with, Cresselia can utilize an effective defensive set with its unique movepool. Moonlight is used as the primary healing move and as such will be used a lot of the time. It is important to note that Moonlight has its shortcomings; it heals less health in sand and rain and has limited PP. Because of this, it should not be used excessively. Psychic is the main STAB move and allows Cresselia to chip down opponents and hit Fighting-types super effectively. Despite its slight nerf, Hidden Power Fire can also work well in this slot. Not only does it dispose of defensive Ferrothorn, but it also gives Cresselia a way to get past Scizor. Ice Beam rounds off the coverage and is a superb move for hitting physically based Dragon-types, Pokemon that Cresselia will often need to wall. Cresselia's final moveslot is dedicated to a status move best fit to the team. Toxic allows Cresselia to spread residual damage and slowly defeat Pokemon, whereas Thunder Wave is best fit for teams that have enough offensive firepower to finish off slower threats. However, Thunder Wave is inferior to Toxic when the team has enough defense to stall Pokemon out. Reflect is an option over either of the moves and enhances Cresselia's ability to take physical hits, allowing it to escape Pursuit more easily and can be used to support teammates.
Source: Smogon
