Unless you have an active sac outlet, Bloodghast is a really bad card. And I do mean sac outlet, not use.
Scarland Thrinax/Eldrazi Monument=Sac Outlet
Quest for the Gravelord/Blade of the Bloodchief=Sac Use
Bloodghast is victim to the same fate as Dash Hopes.
2/1 attacks into a 2/3. What happens? The 2/1 dies and the 2/3 lives. Next turn, Bloodghast comes back, attacks into the same 2/3 and it dies... Again. It will probably keep going like this for a while.
But what if I have something like Quest for the Gravelord that benefits from things going to the graveyard? Well, then they let the 2 damage through and go on with life. In the meantime, you're stuck with an "unblockable" 2/1 and a now useless card.
And because I know that this won't get through 90% of your skulls due to this being the Standard forums, think of this. Every time you draw/play Bloodghast, name a card you'd rather it be without thinking. You should have no problem coming up with a name.