This is a tag-like game.
To begin, the boundaries for play are set. If in a room, the objective would be to get from one side of the room to the other. If outside, a parameter must be set. The smaller the boundaries, the harder the game.
All players begin on one side of the playing area. An octopus is selected to stand in the middle of the playing area. They can run anywhere within the playing area. When the octopus shouts “Octopus Attack!” all players must run from one side of the playing area to the other and try to avoid being tagged by the octopus. If tagged, the player must sit down where they were tagged, and become seaweed. Seaweed may tag other players, but they must do so from their place on the ground. They may stretch and reach, but they must start from a seated position. If tagged by seaweed, the tagged player also becomes seaweed in the place they were tagged.
Once the number of players dwindles to a few, the octopus may shout out “Tidal wave!” in which case all seaweed can stand up and chase players to tag them. However, they must sit where they are when the players reach the other side.
The game ends when one or two players remain, or when you are out of time.