Heres something I have been thinking of... why is it cheaper to use a creature with an ability (unlimited usage) vs a spell with the same ability (up to 6 uses).
Creature that can use the ability more effective
Anubis vs Quint (Dual Element)
Fallen Druid vs Mutation (Dual Element)
Air Nymph vs UG
Death Nymph vs aflatoxin
Nymph Queen vs Nymph Tear
Purple Nymph vs antimatter
Life Nymph vs Epinephrine
Creatures that are the same
Trident vs EQ (Dual Element)
Black Nymph vs liquid shadow
Turquoise Nymph vs quint
Gravity Nymph vs Gravity Pull
Spells that are cheaper
Explosion vs pulvy (Dual Element)
Freeze vs Arctic Octopus
Precog vs Golden Nymph
Rage Elixer vs Fire Nymph
Now, you may say that a creature requiring a second element to use its ability is a downside, so its ok for the ability to be cheaper. But I disagree with you. Take Pulvy for an example. I have a deck that is mainly Earth. I also want some Perm control in my deck. I decide to add in a pulvy. I also need to throw in a gravity mark/tower/pendulum at the least. So I do that. Now I have almost unlimited perm control. I may occasionally be delayed from lack of quanta, but thats ok. Waiting one turn wont always kill ya. Why is it that pulvy is usually picked with its 2 ability cost instead of just splashing fire with its 1 ability cost? Because, it can be used infinite times.
And you worried your creature/permanent is going to die when you place it? Well, thats a matter of risk vs reward. If they dont have CC/PC then that one creature is going to do a whole lot more than just 1 spell
I understand nymphs wanting to be useful and stuff, so you could consider those exceptions, but I think as a general rule of thumb, the spells should be cheaper than the abilities.
