You need to collect all the cheese on the level to complete it. You can see a counter near a counter with lives.
+ you get 3 bubbles from a candy instead of 2.

File: Tom & Jerry (and Tuffy) (U) [!].nes
CRC32:  0xd63b30f5
MD5:  0x716dd6985bc80a3c547cc84b2c8d75e4