Maybe Contagion Engine? It's a better contagion clasp. Also, even if it is a bit off-theme, in a 4-color deck : Chromatic Lantern.

Karzalar - I didn'r put Contagion Engine for some reasons, it's a bit expensive in my country, it's very high cost and the one II think the most important reason: It's too strong, your friends will never let this on board.Chromatic Lantern is aewsome! but what i should cut??

thanks for your comment!!!

I'd suggest removing a one-time proliferate source, such as Spread the Sickness, which is BOTH costly and slow (5 CMC destroy target creature at SORCERY speed? Ew.)

Also, for 4 color decks goodness : Command Tower, Commander's Sphere, Darksteel Ingot for color fixing, which might be better.

What i'd do :

Command tower replacing a land like Yavimaya Coast

Commander's Sphere replacing Fertilid (since you got like 7 basics total)

Darksteel Ingot replacing Tumble Magnet.

(That's if you have manafixing problems, but always have a Command tower in a commander deck that's 2 or more colors)

Honorable mentions and/or suggestions, if you prefer : Ring of Three Wishes, Darksteel Reactor