Each time you proliferate, youll be further reducing the size of your enemy creatures that have -1/-1 counters on them
If all of them are heads, this attack does 120 more damage
For a card to become a sideboard staple, it either needs to be the single most efficient version of an effect (Natures Claim), have a particularly backbreaking impact on the targeted deck (Stony Silence), or be so broad as to have an impact in multiple matchups (Rakdos Charm)
The format evolves but not in radical ways and the reason behind this is quite evident if you think of it
Typically, theyd end up out-of-position, and it wouldnt be the Ajani Vengeant that killed them but the Purphoros, God of the Forge or Blood Moon that they opened themselves up to because they fought Ajani
In the case of Murders at Karlov Manor , 250 of each serialized card are potentially found in collector boosters