20 tiers would look more impressive, and to avoid losing the division I mentioned above, you could assign 2-3 creatures to each level.
Level 7: Angel, Dragon, Phoenix - indicating top-tier status.
Level 6: Naga, Unicorn, Wyvern - candidates for top tier.
Level 5: Minotaur, Lich, Earth Elemental - good promising players.
And so on. Having 3 creatures per level would look quite good.
Скажу я вам, мои друзья.
Я некромант, я маг великий, и армия моя
Непобедимая, огромная!