Guide To Best Prizes In GG

First of all, they will obviously be from the hardest level Trial of Spheres. If you are able to get a Gold Medal on that, you have a chance to get
800-1200 gold
Major Battle/Damage Elixir
Wyvern Hoard Pack
Dragon Hoard Pack
Green Thumb Pack :)If you want remarkable reagents, you just have to get a silver medal on ToTS, it is really easy.

There is still more. From any Hard level such as Labyrinth, you can get an eye of bartleby pack, getting a silver medal on it
From the easy levels, you can get pets, which is the only thing good from them.