One card has to be at the bottom of the list, and for me, its Lorehold, the Historian (despite it having some amazing artwork)
Kilo, Apogee Mind This kilogram pound robot (thats why its Kilo right?) can do all sorts of crazy things, and while the easiest way to tap is attacking, there are plenty of other ways to do so, and many, many, many payoffs to proliferate that it opens up to be abused and played with
This set added more myriad creatures and introduced cards that spread the ability to other permanents
Not once, like Curiosity, but that much damage in cards
Its not just a tap-creatures-down kinda card, but with Equip 4, you have to be pretty in on tapping stuff down to justify it
II Heavenward Howl When you next cast a creature spell this turn, that creature enters with an additional +1/+1 counter on it