It is just a sideboard card, of course, but one of the best ones ever printed
For the rest, consider whether youd want either half in your deck individually
Also, for flavor reasons, it was nice for the card to actually change ownership
As if this weren't powerful in its own right, at the beginning of its controller's combat phase, it can be used to provide an artifact creature such as a crewed vehicle with both lifelink and vigilance, allowing already impressive vehicles to offer yet even more value
BPhillipYork: This enables a whole deck around discarding and replaying, essentially giving madness to everything in your deck, though, obviously it's mayhem