Undertale Collectables:
Currency: GOLD
As there is no visual representation for Undertale's currency, the icon for this event is represented by a black square with a white border and a pixelated "G" inside.
Pose: A COOL DUDE!
The Mii will pose in such a manner that resembles Papyrus's battle sprite from Undertale.
Pal: The Annoying Dog
This Pal is unique in the sense that it doesn't show up like usual. Instead, it'll pop up from random spots on the Hub to do something to surprise the player such as landing on top of your Mii from above or temporarily stealing your Held Item.
Hub World Changes:
A Smashing New Underground
The tree in the center is replaced by Mount Ebott, the mountain that the player falls into at the start of the story. There's also a Red SOUL hovering above the summit.
The other sections, each with the other six SOULs, are themed after certain areas you can find in the game such as the Bed of Flowers, Waterfall, Snowdin and New Home. Joining the usual NPCs are Undertale's wide variety of Monsters, such as Loox, Chilldrake, Woshua, a variety of Dogs and Tsunderplane among others.