You can find out the rarity by looking at the bottom left symbols: common (circle), uncommon (diamond), rare (star) there are also holofoil/shiny versions called holo rare and reverse holo rare
Still, if you don't already have the rare duals, replacing them with Contaminated Aquifer and Dismal Backwater is a fine plan for the short term, although in the long term, you'll probably need to upgrade to compete at the higher ranks
How many SIRs in an ETB, display, or bundle
Once youve hit six Ink in your Inkwell, Ruby/Amethyst starts to get scary strong
Deconstructing a Magic: The Gathering Card There are eight major parts of a Magic: The Gathering card that allow players to understand how it is played, how rare the card is, and more
For my take on the topic I thought I'd explore how we chose to do color-shifted cards as our timeshifted cards