Against Physical Attackers:
* Blissey: Blissey is the classic wall, with incredibly high HP and Special Defense. It can tank most physical attacks and heal itself with Soft-Boiled. However, it's weak to Fighting, Ghost, and Dark type moves.
* Snorlax: Snorlax is a great choice for its high HP and Defense. Its Curse ability lets it boost its Attack and Defense further. It's weak to Fighting and Ghost type moves.
* Skarmory: Skarmory has excellent Defense and Special Defense, making it a great mixed wall. Its ability, Sturdy, protects it from OHKOs. It is weak to Fire, Electric, Rock, and Ice type moves.
Against Special Attackers:
* Cloyster: Cloyster has incredibly high Special Defense, and its Shell Armor ability prevents it from being crit. However, it's very frail physically and vulnerable to Fighting and Rock type moves.
* Forretress: Forretress is another good option against special attackers. It has high Special Defense and boasts an impressive defense stat. However, it is weak to Fire, Water, Fighting, and Ground type moves.
* Slowbro: Slowbro, with its high Special Defense and Regenerator ability, is very difficult to take down. It is also a powerful special attacker, but it is weak to Fighting, Ghost, and Dark type moves.
Other Considerations:
* Type Matchups: Choose a wall that resists or is immune to the types of attacks you expect to encounter.
* Moveset: Make sure your wall has moves that allow it to survive and potentially even counterattack. Consider moves like Toxic, Protect, Reflect, or Light Screen.
* EV Training: Maximize your wall's stats by strategically allocating EV points to HP and the relevant defensive stat.
Important Note: While these are solid wall options, there are other Pokemon in Emerald that can function as walls depending on your specific needs. It's important to consider your team composition and the Pokemon you're facing when choosing a wall.