BubbleBeam is a Water-type move. The Pokémon shoots lots of bubbles at the opponent, dealing mild damage. It's difference is not much known yet from the similar attack, bubble. Only the name, how much damage it causes and how many bubbles are the only known differences.
Most water types can learn it, (Staryu, Mudkip etc.) but Mew can also use it. Piplup can learn the move once it has evolved into Prinplup.