Thanks for the info Caerith and J0dy77.
I'll farm it just to grab the Sky Dragon. Not for utility but it's impossible to resist collecting it up. At the very least I'll do all difficulties to get the stone.
Hopefully it will take less tries than the red Sky Dragon which stubbonly refused to drop for me until I'd run Master 15 times. At least the exp and money was reasonable despite the 50 stamina cost.
I spent the weekend powerlevelling on Tower of Giants to raise my team cost and stamina pool and grabbing pengdras to level up my Parvati and Dragon Knights. Sorry any gaffers on my friends list if you found my leaders useless! I only got her to lvl 28 but plan on evolving her and my knights to ADK as soon as possible. Then I'll level my red team further.
Now I have the red Sky Dragon is there any point farming Sky Dragon for another Naga? I have one I'm levelling up now but I was wondering if two would be useful in some situations?
Monsters I have are:
Red: Shiva the Destroyer, Shiva, max skill Gigas, Phoenix Knight, Mystic Flame Knight x 2, Echidna, Meteor Volcano Dragon, Kagutschi, Firedragon Tyrannos, Drall, second unlevelled Titan, red Sky Dragon.
Green: Parvati, Dragon Knight x 2 (one nearly at ADK), MSK, Green Odin, Marine Rider x 2, Alraune, Sylph, Toytops, Dragonette
Blue: Lakshmi, max skill Siren, Beast Rider, Fenrir Knight, Icedragon Plesios, Aurora Dragon, Red Ice Leviathan, Undine, two more unlevelled Mermaids.
Dark: Vampire Lord, Dark Dragon Knight x 2 (one nearly CDK), Lilith Witch of the Night, Gryps Rider, Pierdrawn, Chaos Devil Dragon, Annihilate Mech Hadar, Wooden Dark Tiamat, Succubus
Light: Valkyrie x 2, Verche Knight of The Sky, Verche, Lightning Holy Dragon, Archangel, Angelion, Genie
I've been really scattershot so far levelling my monsters and I'm trying to get more focused now I have some team compositions in mind.