Toothless will glow in the episode "The Night and The Fury"
The Skrill will be at war with Astrid in the episode mentioned above. As a glowing Toothless is seen catching Astrid and colliding whith a Skrill.
The Screaming Death wil be related to the Whispering Death or a WD and Red Death hybrid as it looks like a WD, but has a RD frill and chin.
The "Giant FireWorm" might be like a "Queen Bee."
The Strike Class dragons might have the ability to glow as Toothless and a Skrill are seen glowing the color their shots are. Skrill is blue as Toothless is purple.
Meatlug will go rogue in "The Iron Gronckle" as Fishlegs is seen riding Toothless with Hiccup and Toothless fires shots at Meatlug.
Alvin might have created an army of Whipsering Deaths.
The Whispering Death and the Screaming Death will be natural enimies.
The Screaming Death will be a "Myth" like the Smothering Smokebreath.
The Screaming Death will be a Mystery Class dragon.
The Screaming Death might also fire a sonic blast hence the "Screaming" in its name.
Gobber might get the Deadly Nadder in the Season finale of Riders of Berk.
Gobber might also get the Screaming Death.
The Skrills fore might not be lighting as Astrid hits the Skrill's breath away with an ax.
We see Snotlout and Hiccup ride Toothless in a cave and another clip of a giant FireWorm with Hiccup, Toothless, and Snotlout watching it. There are also "Flaming honeycombs" so maybe the Giant Fireworm queen will be in the same episode Hiccup and Snotlout go in the cave.