My rough heuristic of creature mana values:
- 0 - usually an X spell. May be cast occasionally to trigger Glimpse of Nature effects and then immediately die.
- 1 - I don't care if it dies, or I'm intentionally playing it as sac fodder.
- 2 - I don't mind if it dies to a board wipe
- 3 - I'm sad if it dies to a board wipe, but okay if it trades for 1:1 removal
- 4 - I expect it to generate some incremental value before dying
- 5 - I expect it to generate some value immediately, or significant value if it lives a turn cycle
- 6 - I expect it to generate significant value immediately, or threaten to generate massive value if it lives a turn cycle
- 7+ - I expect it to generate massive value immediately, or threaten to win the game if it lives a turn cycle
...although I will note that if I'm playing 6 or 7-drops, I usually expect to either be ramping into them or cheating them out. 5 mana is pretty much the limit for 'I expect to cast this by naturally playing a land every turn'.
That said, power creep has meant some of these benchmarks have dropped by 1-2 mana - cards like
Chulane, Teller of Tales and
Golos, Tireless Pilgrim certainly punch into 'win the game if you untap with them' territory. I do think those are outliers though, and most cards fit into the above categories (although the outliers certainly represent a larger percentage of actually-played creatures, and will represent a larger percentage of the format over time).
edit: another way to think about this is risk vs reward. If you cast
Elvish Visionary or another cheap creature, you essentially have zero risk, but also not much reward - two mana for a body and a guaranteed card is consistent but unexciting. If you cast
Beast Whisperer, you're increasing your risk level - you don't get anything immediately, and four mana is a much higher cost that can leave you at a disadvantage if an opponent has
Doom Blade to answer it. However, you also get a much higher reward if it sticks around.
As you go up to 6 or even more expensive cards, the ones that see are either ones that
generate value immediately or
protect themself (and thus have a lower risk) or represent a
higher reward if they survive.
Anyway,
Ajani, Adversary of Tyrants seems... meh? The (+1) is fine if you're a dedicated +1/+1 counter deck, but unexciting otherwise. The (-2) is okay, but if you're doing it twice I would prefer
Call of the Death-Dweller. The ultimate is good (particularly in aristocrats / go-wide decks), but not something I would count on outside
Doubling Season shenanigans.
