The happiness button has disappeared from the NPC dialogue menu in the secret seeds. The only secret seeds I tried since the update are the 'getfixedboi' seed and the 'dontdigup' seed.
Edit: The button seems to be there in every normal world
My favorite has to be either the Brain of Cthulhu or Duke Fishron. Both are very cool bosses (Duke is a pig, and pigs are my favorite animal), but if I had to pick one, I'd choose the brain. The Crimson is my favorite biome!
My least favorite mini-boss is the Ice Queen. She's just a little...