In Grixis Affinity why 4 Ichor Wellspring and not 4 Cryogenic Relic? | tcgmode

Exactly the title, why 4 \[\[ichor wellspring\]\] and not 4 \[\[cryogenic relic\]\]? They’re essentially the same card except Cryogenic Relic costs one blue. When they enter or leave you draw one, but you can have also pay blue and colorless to tap a creature. It’s a better Ichor Wellspring, and ...