It won't be able to if Slash Dragon wasn't properly Summoned first. (Which, for Slash Dragon, means being Fusion Summoned.) So if you Summon it with a card like Cyber-Stein, Summoner of Illusions or The Dark - Hex-Sealed Fusion's Tribute effect, you won't be able to revive it.
Most Fusion monsters must be summoned properly first before they can be revived from the Graveyard. That's part of the basic rule for Fusion monsters :)
The only exception is Fusion monsters that states they cannot be Special Summoned in any way except by a Fusion Summon. In that case, even if you Fusion Summoned them properly, you still cannot revive them.
Anoymous
Anonymous
