It did exist. I think I have it on tape somewhere. It’s where the wind blows and the howlers start howling and the grumblers start grumbling and the little boy Ukariah goes off from his family to stop the wind. He meets the Grinch and the Grinch shoves him down into his sled where a 30 minute acid trip commences.
There were in fact three Grinch cartoons: How the Grinch Stole Christmas, Halloween is Grinch Night, and The Grinch Meets the Cat in the Hat (I’m not sure I have the titles exact). Speaking as a cartoon character myself, trust me when I say the latter two are far inferior to the first one.
On the other hand, The Cat in the Hat and The Lorax weren’t bad. And if you find a copy, the Warner Bros. Looney Tunes version of Horton the Elephant is very good.
The title of the last one is The Grinch Grinches the Cat in the Hat. The original title of Halloween is Grinch Night was It’s Grinch Night. The Warner Bros. cartoon is Horton Hatches the Egg.