Activating a Walking Ballista is nice because it represents an extra point of power and toughness and well as an additional point of damage that can be thrown around at the Constructs owners discretion, but four mana isnt a small amount
Then, through proliferate, these counters grow and grow until the Creatures theyre attached to inevitably die
You play Fabled Passage to get some extra utility from Mayhem Devil and Bomat Courier does the same thing
Primal Vigor and Parallel Lives can double your Cat token output
There are, of course, a bunch of cards that I don't have much interesting things to say, and some whose jokes might fly over my head
When Wizards prints cards like Xathrid Necromancer, Voice of Resurgence, or the newest addition Ashcloud Phoenix, they have my attention