Cards like Tropical Island are between two and three times the Beta price, while as we slouch down toward Armageddon, its still almost double the Beta price
One life for each creature adds up quickly
Death and destruction flavor this form of mayhem
These rely on Amethyst cards featuring Merlin and Madam Mim, who trigger effects when cards enter and leave the battlefield
Mechanics arose from visualizing how two armies of creatures would battle each other, rather than creating mechanics and then fitting them into the Magic world. These two points of departure were later codified in design terms as top-down versus bottom-up
Nethroi, Apex Of Death can trigger this effect multiple times since green, black, and white generally have the cheapest mutate creatures, and Nethroi's ability triggers whenever it mutates, not just when it's cast