Added C'thun and Dragon packages
Basically this is the base outline of the deck, add extra cards/packages from the following. Of course you don't need to add all the cards given in a package, but be careful not to cut too many cards or that package overall will be weak. Some packages are smaller than others so you can run up to 3 packages. All cards are ordered in decreasing power level. Also be aware of the additional possible interactions between the cards (for example doppelgangster - evolve).
I will gladly consider the package ideas you post in the comments.
This package took significant hits with the recent nerfs, but is still decent.
Additional notes about this package (expand the spoiler):
There are numerous elementals already in the deck, in other packages and in additional card options (zeph, grumble, jade spirit, bog slosher, siamat, etc.), so consider your picks from this package in addition to these. Try to put a reasonable amount of elementals since "if you played an elemental last turn" becomes a hard condition to satisfy without them. Harbinger's power level goes up significantly the more elementals you have and the more greedy you can be with them. Overall this package is pretty weak compared to others, so don't expect much.
Firetree Witchdoctor, Netherspite Historian, Scalerider, Twilight Guardian, Twilight Drake, Big Ol' Whelp, Blackwing Corruptor, Cobalt Spellkin, Dragonmaw Scorcher, Hungry Dragon, Brightwing, Lightning Breath, Frizz Kindleroost, Scaleworm, Crowd Roaster, Primordial Drake, Azure Drake, Twin Tyrant, Nithogg
Also you can check out the variant I have posted before and inspired me to create a guide in a different format like this in the first place: Galakrond Evolve