Both of these are worthy of being a three-mana spell on their own, but having them both on one card makes this a great card against a lot of different decks, and you can play it without worrying about what it is your opponent might be doing
That said, if you're able to part with one of your precious cats and flip him over, you'll find Ajani, Nacatl Avenger is no slouch in planeswalker form either
As the game progresses and cards are discarded, the probability of drawing an action card changes
(A player with ten or more poison counters loses the game.) The contagion spreads and the Multiverse quakes
For the record, a Foil version of the Karn Liberated, also covered above, fetches nearly $800 too, making these foils demand a serious premium