If I may, I'd like to offer a fun idea for the group to do together.
There's obviously fire elementals in game, and there's also plant based characters, ice based creatures, and if you squint I think you can find a rock themed one hidden in waterfall, and there's some water based creatures.
But what about a direct opposite to Fire elementals like Grillby, Fuku, and Heats Flamesman? What about a Water Elemental?
My idea, is for people to interpret what they think a water elemental in Undertale may look like, and act like.