Grinexx is the boss of Turtle Rock in A Link Between Worlds.
The battle with Grinexx has two phases. In the first phase, Grinexx swims in a lava pool underneath Link, and Link must drop blocks of ice on it using the Ice Rod through holes in the floor.
In the second phase, Grinexx comes out of the lava and fights Link. Grinexx tries to attack Link by either shooting out his head using his spring-like neck, or he curls up in his shell and randomly rolls around the arena. He also occasionally releases an explosion. To damage Grinexx in this stage, Link must attack Grinexx's head using the Master Sword. A tip to damage Grinexx in this phase is to freeze the pillars of lava with the Ice Rod and merge onto them, so when Grinexx shoots his head at the hero and hits the pillar, he is stunned for some time where Link can freely attack him.
After defeating Grinexx, Link can claim the painting of Sage Impa.