Wouldn't all or most of the Nymph names sound better if the upgraded and unupgraded names switched around? The upgraded names sound really basic to me personally.
Unupgraded | Upgraded : Notes
Turquoise Nymph | Aether Nymph : Switch
Blue Nymph | Air Nymph : Maybe for this cause changing the upgraded name to "Azure Nymph"
Black Nymph | Dark Nymph : Well, this seems okay.. unless you want to add some stone or gem name like Onyx Nymph
Grey Nymph | Death Nymph : Seems alright.. Any ideas of improving this one? I'm stumped.
Auburn Nymph | Earth Nymph : Switch
Purple Nymph | Purple Nymph : Maybe from Purple Nymph to Violet or Amethyst Nymph?
Red Nymph | Fire Nymph : Maybe change "Fire" to "Crimson"?
Amber Nymph | Gravity Nymph : Switch
Green Nymph | Life Nymph : Maybe change "Life" to "Jade"?
White Nymph | Light Nymph : Seems okay.. unless you want to add some stone or gem name like Opal Nymph
Golden Nymph | Golden Nymph : I like "Golden," but maybe make the unupgraded "Time Nymph"?
Queen Nymph | Water Nymph : Switch, this one bothers me the most.
No suggestions mechanical wise, all just aesthetics.