Lucifer Likes to Smile is the sixth stage in Ritual Happiness.
Though intimidating to new players, this level is easy. The secret is MASS MEATSHIELDING. Get Macho Cat, Wall Cat and Samba Cat (or any other meatshield) and flood the stage with them. Also pair them with strong long ranged units like Sexy Legs Cat, Dragon Cat and Paris Cat. Do not use Ufo, it is too expensive for what it does. Mythical Titan can soak up some blows from the Sloth.
Let's say you know how to play the game. Let's say you are playing this stage because you need Evil Cat and started playing on March 2nd or something. What do you do?
Well, it is still simple. While there are no non-gacha units capable of striking THE SLOTH with impunity (though Bahamut has around the same range and Ururun is just a little in), by now you should have a good long ranged unit. Hacker Cat, Megaphrodite, InsertLugaHere, Super Galaxy Cosmo, etc. etc. anything with over 450 range works. Even things with under 450 range should work if they are strong enough. Diabolic Gao makes mincemeat of everything on this level. Just apply 2 meatshields (if one is crazed cat or crazed wall) or 3 if you don't have the Crazed yet. Crazed Sexy Legs Cat can be useful as the level 3 wave lets it reduce peon density while your melee attackers move in.
Note: You need to have Li'l Eraser Cat or any equivalent substitute, or just bring a lot of meatshields. The amount of knockbacks other Special or Rare meatshields have is usually more than one, which can be a problem when trying to prevent Lucky Sloth from advancing.
Execution: Start the battle and push forward, only using Cameraman and Li'l Eraser. It'll be a slow push so you can raise your money count. By the time you reach the base, you'll have about a full Lv.8 wallet. Once Lucky Sloth comes out, let it kill your remaining cats. As it comes closer to your base, spam all your units. The Cameraman Cats will defeat any Mooths in the way and Ururun and Bahamut will take care of Lucky Sloth as they outrange it. Soon enough, Lucky Sloth will die and you can destroy the base.
Don't overthink it just because it's a 4-Star Stage. It's a little harder due to not having better meatshields available to you, but that's the only hinderance preventing you from beating it.