pokémon center pikachu promo card BW-P Promo 120/BW-P Tohoku which is a Japanese Scarlet Pokémon × Van Gogh Museum:

Cavern of Souls and Mana Crypt are currently the only cards with cosmium ink versions

Four Knocks, basically a white Phyrexian Arena with an expiration date

Then we have some that combined types like Daru Warchief

One thing to note about Prophetic Prism in UW Blink: It not only facilitates much needed card advantage but can also fix our mana, and you may have noticed

The other option which is slightly less value but more reliable and cheaper CMC is Gluttonous Slime , this doesn't have the card draw but is an instant speed sac outlet

Here are a few questions you should ask yourself when evaluating Planeswalker cards: Does the Planeswalker protect itself