The opponent is hit with an energetic force blow. In addition, heavy rocks can be moved with the attack. In Johto HM Strength is not needed in the Ice Patch, it is sufficient to simply address the stones with spacebar and they move.
In Unova you need HM Strength in the endgame, you can find it here.
An item that use the move Rock Smash outside of the battle. Can be in all Lootboxes (Blue or Red) as a very rare item or as a random item in the 40€ LootBox Packet.
