Pako

Pako (generically referred to by Nintendo Magazine System as an octopus ) is the boss of the Turtle Zone in Super Mario Land 2: 6 Golden Coins, in the belly of a whale.

Super Mario Land 2: 6 Golden Coins
Pako will attack Mario by swimming around releasing its offspring. The little ones will home in on Mario, while the parent swims left and right across the arena. In order to defeat Pako, Mario has to hit its head three times, which can be difficult, as the entire battle with Pako takes place underwater. Alternatively, Fire Mario can defeat Pako with six fireballs. The smaller octopodes, Poko, cannot be harmed, and are the most dangerous threat in the battle.

Mario vs. Wario
Pako (referred to by Mario as a monster octopus) also appears in the Mario vs. Wario comic, which is a loose adaptation of Super Mario Land 2: 6 Golden Coins. It attempts to attack Mario while he is crossing a lake, but is stopped when Mario asks what an octopus, a saltwater creature, is doing in a freshwater lake. Pako ponders this and then exclaims that must be why it has not been feeling well. Mario offers to pour some salt in the water for Pako, but accidentally pours sugar instead. It is last seen lying face down in the water, unmoving.