Final answer:
In the episode 'Hide and Seek' of Bluey, the toy Bluey finds under the sink is called Smudge.
Step-by-step explanation:
In the episode 'Hide and Seek' of the TV show Bluey, the toy that Bluey finds under the sink is called 'Smudge.' Smudge is a small blue dolphin toy that belongs to Bluey's friend Rusty. It plays a key role in the game of hide and seek that the characters are playing.