Pit of Offerings is an underrated cave that is occasionally better than Bojuka Bog due to the mana fixing it can provide, so it doesn't quite make the ranking, but is a great option if you only need to hit three or less graveyard targets
Trascendent Dragon is Fractured Identity (yes, I'm aware of counterspells that do this, but no one plays them) on a dragon
The former one puts a three or fewer cost permanent into your hand but if you are the Monarch into play
Ral, Monsoon Mage / Ral, Leyline Prodigy Ral, Monsoon Mage is fantastic on its own as a quick way to cut your spell costs and is a Birgi, God of Storytelling away from storming off
While not single-handedly fixing all the issues with the color combination, Avacyn brings a truckload of value to the table and lets us play Boros in a way that has never been previously supported
When you counter a spell on the stack, it has no effect and goes straight to the graveyard