There are a lot of creatures in Standard that get +1/+1 counters whenever you gain life, and these Historic decks look to capitalize on that while using the powerful green instant, Collected Company
He liked the idea of creatures that got better when your opponent's life was below a certain threshold
When Elenda's Hierophant dies, create X 1/1 white Vampire creature tokens with lifelink, where X is its power
In other words, we get 3-4 mana worth of value each time we cast a noncreature spell large enough to draw two cards (not to mention Hero tokens)
There is one old Wall which allows you to Attack with it, Mobile Fort
UnStable used watermarks as a new and improved version of that mechanic, neatly associating any diverse group of cards with minimal awkward templating or visual clutter