Elaborating on each (incase i don't remember exactly): -Asgore is relevant - This should be obvious -Dess lore - we get revealed on the dess incident -NOT final shadow crystal fight (ch6) - the secret boss (if one) won't give you the final shadow crystal. this would be in chapter 6. -Asriel comes back - this is obvious twin -Knight seen in beginning of the ch - this is obvious also -Ralsei solo secret boss - obvious -More Toriel & Sans things - MORE sansriel (and hopefully kris obviously getting angry at sans) -Weird Route Relevance (IN DW) - Weird route is in the dark world. Like using iceshock again (and not just a cutscene like ch4) -Rudest Buster - new battle theme for enemies regularly appearing -Noelle joins the party - specifically in the dark world -Knight seen in end of the ch - obv. -Fountain opened at end of ch5 - someone opens a fountain (similar to end of ch2). bonus points if it's noelle -Shadow crystals purpose revealed - obv. -Woody theory 3 is true - watch spookydood's video. basically a woody-esque character would be the secret boss. -Ralsei's object is not revealed - obv. -FRIEND spotted again (not boss) - we see friend in the shadows again -Shadow crystals purpose revealed - obv. -flowey-esque boss - obv. -Fallen humans inspiration - fallen humans miniboss based off of the flowers that look like the fallen -Jockington gets a fake beard - saw this in a post on another site, but jockington makes a beard out of cotton candy. -More than one dark world - obv. -Mad Mew Mew returns - obv. but as a darkner -BERDLY IS BACK!! - THE GOAT RETURNS! in both routes too -New soul type (not in ut) - new soul that wasn't in undertale -Asgore is tricked by the villain - obv. but bonus points if it's the flower-esque boss i mentioned