That pegasus in my Kelpie Headcanon here is Ophiliaflowers 's ponysona Sing-A-Long being licked by Finnigan. Whilst I was making this in stream, Scoob was sayin he was handsome so I SHIPPED THEM SO HARD.

Here's the low down:

Sing-a-long is on vacation with some friends and decides to go float on a nearby lake to chill.
Whilst chilling local and secret kelpie is swimmin round and thought that- in her smol stature- Sing-a-long was a swan and went to go check, with his tongue.
She freaks out- of course- and flies away.
Finnigan tries to call to her to apologize but she's long gone.
Later: Finnigan sees Sing-a-long walkinga round town with her friends and recognizes her.
Much to his reluctance, he apporacehd her and tried to apologize- which she promptly had no clue what he was talking about and it doesn't help that all she can think is OH MY SWEET CELESTIA HE'S A HOTTIE
Pen Rose sees the two and assumes they are flirtinga nd invited Finnigan to go swimming witht them.
He tags along but doesn't go in- for fear of being seen as a kelpie.
Sing-along: "What's the matter? Can't you swim?"
Finnigan: "Uh course Ah can Ah'm jus- uhm-"
Sing-a-long: "Then go on"
She pushed him in and giggles as he falls right in face first. But he doesn't come up.
Sing-a-long freaks and dives in to "save" him and is met with a very familiar face. He apologizes again, but now she gets it barely- past the thought of HOH SHET HE'S HOT NOW TOO
Unbeknownst to the two- kelpies have a lil bit of hypno magic and go all Shape of Water, leaning in for a kiss. They make out for a while until Sing-a-long passes out cuz she can't breath underwater like he can and wasn't concerned with suffocation whilst gettin her magical mack on.

love ya scoob
now the worl knows of your many ships