When Tim Curry's voicing an animated villain, you'd be a fool not to let him sing. So he does in the episode "A Little Evil" in a most villanous lullaby from the Evil Manta to his son.
Go to sleep
My rotten little ray
And dream of dark and evil deeds
For instance, wouldn't it be fun
To be scatter scallops with a glare
Make the grunion run
Around the lionfish's lair
Time to hit the sack
My brooding little brat
For one day you'll be feared from sea to sea
When you're worst, you're at your best
Close your eyes, you need your rest
If you want to learn to be just like me
You're the most deplorable
Horribly adorable
Manta that a daddy's ever seen
Have a real bad night
Give those beddie bugs a fright
It's delightful when you're spiteful
I'm so proud I want to scream
Rest your wings
My precocious little pup
Relax in peaceful misery
Drift away and pretty sooner
You'll be terrorising tuna
Just remember, being wicked is the key
If you want to learn to be just like me