For me this conjuration is only good for finishing an opponent.
If the game will last a few more rounds, I would not try to waste my dying creature to improve my hit on one of my other creatures.
The reasoning is. I played multiple tournaments on other games, that last sacrificial lamb is very important to do one of the following - tie up your opponent (hinder), harrass or do one more ping on your opponents life.
By safricing the creature, you lend your opponent to concentrate more on you or your other creature. I want them to sacrifice and waste additional action killing the guy. If they don't then they will get hit back.
Wasting of action is key in winning this game.
For me this conjuration is not that great at all. An extra pair of hands with their own gun in a battle is better than killing your guy and getting his gun to improve your chances to hit your opponent with two guns.
My 2 cents.
I think the card has uses, namely if you can time it just right so that the creature is going to die anyway before its next activation and you sacrifice it to boost another creature's attack. At least that way you get some last use out of the creature before it dies.
However, I think that the set of circumstances where this card is good is so narrow that it becomes an unreliable card. It's got potential, and certainly
could win the game for you on occasion, but there are just SO MANY other cards to play that are more likely to pay off that it can be hard to justify the action.
Another problem for this card is the "when do I play it" question. If you play it early, you are slowing your offense by an action, and those early actions are pretty key in setting up those powerful in-your-face beat-down assaults that rely on tempo and pressure. If my opponent stalls his in-your-face assault by an action, that's one more action I have to prepare for it, which is a big deal.
If you cast it mid to late game, when you are within striking distance of the other mage, then you are spending an action to set up
potential damage in the future instead of just causing
actual damage immediately.
Eh, like I said, it has it's uses, but I doubt it's going to see extensive play or be a huge game winner when it does. Unless of course they start making some cards like I talked about that have abilities that trigger off of creatures leaving play. Then it could be quite the combo card.