Any cheaper than that and this starts to become absolutely ridiculous
Before Wizards of the Coast released the Alpha Edition of Magic in 1993, they used Gamma Playtest cards to develop the game
Unholy Heat Unholy Heat is an interesting case: As long as you can fulfill its delirium clause, this red instant deals so much direct damage that it's basically unconditional removal something that red doesn't usually have access to, and which makes Unholy Heat a bit of a color pie break
It also comes with a kicker cost of three generic, one blue, causing your opponent to mill half their library rounded up
We can take a card like Isamaru and say, "if this card on turn one does either too much or not enough on a regular basis, there may be aspects of my card pool worth reviewing." Heed this lesson, fellow Magic thinkers and constructors of Magic experiences: establish some barometer cards for your project
Arena being a free-to-play game makes trading more difficult, though