The major differences between Lazav and Cemetery Puca are where this guy really shines, however. First of all, Lazav can copy a creature when it is put into a graveyard from anywhere! This includes being discarded from the hand, being milled from the top of the deck, or even being sent to the graveyard (like by a Life’s Finale effect) that sends creatures from your opponent’s deck to the graveyard. Also, unlike the Puca, his ability costs you nothing, where Puca’s ability costs you one colorless mana each time. Finally, the copy that Lazav becomes gains hexproof, which is especially interesting.
About the only downside to this card is that the name remains Lazav, Dimir Mastermind and it is still Legendary. So, you can only have one on the board at a time. To be honest, though, to have an ability as great as his, being Legendary is perfectly fine and understandable. Keeping the name is just a part of that Legendary aspect. Also, because of the Legendary rule change from Magic 2014, an opponent can’t simply get rid of Lazav by playing a Clone effect or another Lazav (as you could when he was first released). The idea that Lazav can copy not only your best creatures and your opponent’s best creatures, but also has hexproof makes this a pretty valuable weapon in any blue/black control deck, including Grixis (red/blue/black).
Lazav is especially great if you plan to use him in as a Commander. You may have your Sheoldred, Whispering One hit the graveyard and have Lazav copy her. Because of the fact that the new Sheoldred is actually called Lazav, you then have a way for Sheoldred to come back. Suddenly, you have two Sheoldred triggers every turn! In Commander, he just has so many ways to copy your own Legendary Creatures’ effects, including being able to potentially control two Olivia Voldarens (in a red/blue/black deck) or two Oona, Queen of the Fae. There’s a lot of shenanigans that can go down with this guy.
While his double blue and double black casting cost may not make him quite as versatile as his Modern counterpart, Cemetery Puca, they could certainly complement one another in a Modern deck. Lazav hasn’t yet found his way into a Standard deck, however. There’s a possibility, though, that he may see play with Phenax, God of Deception, as he provides 4 devotion and can actually copy Phenax or other Gods like Thassa, God of the Sea and Erebos, God of the Dead! He could be quite the force in that sort of deck, allowing you a bevy of options that you could have only before imagined. He’s still one of the most underrated mythic rares in Gatecrash, and he’s a greatly under-utilized Commander card, as well.
Don’t be surprised if he shows up in blue/black Tempo/Control in Modern at some point. After all, who doesn’t want two Vendilion Cliques? Probably won't happen, but it would be pretty neat!