Thanks to Grandpa Slib for starting this list and all others who contributed. (View Forum Topic)

Sprite	Name	Spawn Time	Spawn Location
	Wild Slime	Night	Fert Island. You find it up a ladder guarding a red chest.
	Wailin' Weed		Randomly appears when you approach the large flowers on the last island. Using whistle on the peak right before Fert's shrine will give you Wailin' weeds at night
	Trap Box		Right near the end of the final dungeon in a chest. It's one time only scout, so if you miss it, you'll have to get it the hard way, through breeding. And one of the monsters require is needed for other stronger monsters, so it's a pain to waste it on a trapbox. I was one of the lucky few to get to scout it first try. Just make sure you go in prepared with monsters with psycho trait and high attack.
	Spitnik	Day	Radomly during the day at the jetty to the old made's island.
	Skelegon	Night	Xeroph Isle; beside the battle stadium in the 'bowl' of the island.
	Seasaur	Night	Palaish Isle; in the pool at the top of the ladder near the Scout Post.
	Notso Macho	Day or Night	Celeste Isle Shrine; found in two different places, in the Sun Tower near the first mirror you find that teleports you to the Moon Tower, and in the Sun Tower on the way to the Sun Tablet.
	Mimic	Day or Night	Randomly found in brown chests.
	Metal Slime Knight	Day	Randomly across the stone bridge leading to the Jetty on the dead island.
	King Slime	Day	Infant Isle; in the temple at the top of the island where you said the Scout's Oath.
	King Kelp	Night	Palaish Isle; in the pool at the top of the ladder near the Scout Post, you need to enter the water to spawn them though.
	Hell Hornet	Day	Found by a brown chest on Fert. Random.
	Hades Condor	Day	You find it when you can cross the bridge on Infant island
	Green Dragon	Day or Night	Palaish Isle Shrine Level 3; in the main room of the Shrine guarding the entrance to a room with 2 red chests. (Always Present/One-Shot Scout)
	Great Sabrecat	Day	Celeste Isle (South Side); at the top of the cliff that the Scout Post is built in to, near the trees and bush. Also pop up across the bridge. They seem to more likely to appear if you head out from inside the tower down to that area near the bridge.
	Great Dracky	Day or Night	Randomly occures across the bridge on Dracky island.
	Great Argon Lizard	Day	By the hidden jetty on the final island. Also on Argon Island.
	Gorerilla	Day	Jumps down at you from the cliffs leading up to the final shrine.
	Gold Golem	Day or Night	Palaish Isle Shrine Level 2; in the room closest to the Level 2 gem switch.
	Gigantes	Day	Infant Isle; near the giant fire pit. If you come down from the shrine during the day, I always seem to find it.
	Frostburn	Day	Day on the second island, radomly at the bottom of the crater.
	Dragonthorn	Day	In the vines you pass on the way to the second Shrine.
	Dessert Demon	Day or Night	Xeroph Isle Shrine; found by entering a door without the glimmering markings on the floor in front of it. (Always Present)
	Demonrider	Night	Radomly during the day at the jetty to the old made's island.
	Dark Slime Knight	Night	Randomly across the stone bridge leading to the Jetty on the dead island.
	Cannibox	Day or Night	Randomly found in brown chests.
	Boss Troll		Near the start of the cave on Fert island, one time only scout
	Beshemoth Slime	Day or Night	Randomly occures across the bridge on slime island, day or night.