While I'm building my own lineup for Silver League. I noticed that the duo of Gelatinous cube and Venari Seedsmith is very annoying due to high health combined with their passive ability that puts you in advantage as the battle progresses.

I find this combo very effective for Silver I League. 90% of the time you'll win on high mana battle. For Low mana, you can play with Chwala or Flesh Golem(if available).