Regal Delicacy

The pet is a shrunken Queen Slime with a face painted on, and it flies after you on the same wings the boss uses rather than hopping. That makes it better behaved than most followers in tight terrain, since it does not get hung up on ledges or fall down shafts behind you.

It only exists on the hardest difficulty, so a Queen Slime you beat on classic or expert will never hand one over. The fight is cheap to re-summon and short, so grinding it is tedious rather than difficult. Bring enough gel crystals for several attempts in one trip.

King Slime drops the counterpart, and the two buff descriptions are written as a running joke about which of them outranks the other. Later versions let you fuse the two summon items into a single one, which is the sensible end point if you would rather not pick a side.