This deck wants to play the to fling big cost cards into your enemy's face.
To use a Trebuchet you need pairs of cheap minions that you don't mind tapping to use the Weapon instead of attacking. To that end we have lots of generation and low cost minions, especially ones that slow down the opponent or protect your cheap minions a little. The are a simple alternative to this siege weapon. The is another option, and can work alongside the Trebuchet well, thorwing the card you just discarded in the same turn.
As ammuntion for the Trebuchet and Catapult you need lots of high cost cards. Lots of the Atlas is focused on stalling and slowing down your opponent until you can potentially cast these cards, in case you don't find your siege Weapons. You also have cost reducers and ramp options to help afford these big cost cards when you can.
s are just to try and protect your big cost Minions from being Buried.
You can see me use an earlier version of the deck on youtube here: