ITT we make signature moves for Legendary mons without one.
Emerald: "A POKéMON that is made entirely of rocks and boulders. If parts of its body chip off in battle, REGIROCK repairs itself by adding new rocks."

Move: Rock Cycle
Type: Rock
Physical
Power: 75
Accuracy: 100
The rocks around the battlefield assault the target whilst healing the user. The user's HP is restored by half the damage taken by the target.

Basically a Rock type Drain Punch with worse name.