This is for it's first evolution, Shelmet.
Shelmet @ Eviolite
Role: Special Wall
Nature: Calm (+Sp. Defense, -Attack)
EVs: 252 Defense, 252 Sp. Defense, 6 HP
Acid Armor: It increases it's Defense by two stages, which if used three times, can maximize Shelmets Defense stat.
Struggle Bug: If the opponent has a Special Attacker, then you can use this move to lower there Sp. Attack.
Rain Dance: When this move is in play, Shelmets status condition will be removed. This move needs to be used when Shelmets HP is in the Yellow.
Rest: This move restores all of Shelmets HP, but puts it to sleep. When it's Raining, Shelmets Ability will cure it's status condition.
Some other moves to consider:
Protect, Double Team, Encore, Endure, Substitute
Protect will block an attack, which can be kinda useful. Double Team can make moves harder to hit, and most of infinite accuracy moves are "not very effective" on Shelmet. Encore can deal with Special Attackers when they use a status move. Endure can be used to make sure that Shelmet survives, but it's not very useful... Substitute will block all attacks and all status moves, although if too many attacks are used, the substitute will fade.
If you can think of a better move than Struggle Bug, please tell me.