The battle of Mossdeep has often been called the Thermopylae of Hoenn, although if the Spartans had Walrein in their armies, perhaps they would have lived to tell their heroic tale. In this war, an enormous armada of ships and water pokemon bent on subjugation had set sail for Ever Grande City – yet rather than offer battle, the bulk of the Ever Grande navy had taken this opportunity to launch an assault on Lilycove's dockyards. The attack would surely bring the war to a stalemate, provided, of course, that their homes, families, and queen in the virtually undefended capital would not first be taken hostage.
To defend their homes, Ever Grande turned to the narrow straits around Mossdeep, and to the hopelessly outnumbered Walrein corps and their trainers. In a fierce hailstorm which the defenders had undoubtedly created, about fifty Walrein floated in the water, but showed little inclination to go on the offensive. Instead, they swam in front of any pokemon which tried to advance and blocked attack after attack, frustrating enemy officers and pokemon alike, while their helmets and armor did little to protect themselves from the hail. When a Walrein was hit, it usually disappeared like a substitute; if they managed to hit the real thing, hail and leftovers usually soon healed their wounds. Every now and then the Walrein found an opening and used it to freeze or ram a few rivals, but they made little progress; every now and then a real Walrein was taken down, but they never left enough of a gap for the enemy to break through.
The battle went on in this way for nearly a day, until the exhausted Walrein were relieved by the returning victorious navy of Ever Grande.