So something for the Companion app (and Gatherer in general) that I feel could be quite useful is refined mana value searches. In particular the ability to filter by even Converted Mana Costs, odd CMC, and or provide the optional IS/OR options to them.

As an example: This will help search for all cards legal that a Companion Obosh could play in its deck when considering the search even and odd CMC options. While the IS/OR option (obviously allowing us to select two+ options in the case of OR) would allow us to narrow the search further, like one CMC or three CMC.