While he is good he is both too narrow and too weak in comparison to really deserve an A cube slot
His Strength and Willpower are also very low, but he does offer 2 Lore points for questing, which is just another of his redeeming qualities
Legendary Enchantment Color tag templates(None) Mikaeus, the Unhallowed Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.) Whenever a Human deals damage to you, destroy it
It's strong everywhere, but it has enhanced value in archetypes that care about counters generally, +1/+1 counters specifically, proliferate tricks for multicolor brews looking to add loyalty counters for their planeswalkers, four and five-color decks, Commanders with evasion, Commanders with a power that, when increased by 1 get a faster kill, Equipment, Aura, and Voltron decks looking to get in kills with their Commander, and loads more
But, like Skullwinder, there will be many board states in which you can operate fairly freely in order to get what you want