Hmm. Unlike Blessed Avenger, Deity of Secrets etc, this one doesn't actually do anything unless you have black mana. It repeatedly untaps, but those untaps accomplish nothing. Perhaps let it have another ability, to tap to deal 1 damage or grant something first strike, maybe? That doesn't cost black mana, so that this has some use in mono-white decks like Blessed Avenger does.

good idea

This looks pretty powerful at a glance. I have to break it down to think about how powerful it actually is:

1. Cast it.
2. Tap it during your opponent's end step to make a token.
3. Tap, pay , and sacrifice the token during your next turn (having attacked with it if possible) and you draw three cards and gain three life. Not bad.
4. Opponent's next turn passes; this is still tapped.
5. Your turn; untapped, but we don't want to tap it yet if we want the cards. It's viable to pop out a token and attack, though.
6. Tap during opponent's end step for a token.
7. Sacrifice the token for 3 cards and 3 life.

So over the course of 4 of your turns, you've drawn an extra 6 cards and gained 6 life. Is that fair? I don't know. Probably? But then there's the fact that this is very efficient artifact token production, which doesn't happen often, and that you don't have to be sacrificing the tokens themselves... It's interesting, at least, and probably fair.

Hilarious to drop this turn 3, then turn 4 cast Phyrexian Dreadnought and sac it in response, to draw 12 cards and gain 12 life :D

But yes, the token-making is a bit more efficient than we normally see. I guess it's not as good as Rakka Mar, though. Perhaps needs some cost on the first ability. (It has accomplished its goal of making this card useful in mono-white or mono-red, though!)

By the way, is Unstable a creature type...?

nope. The name of the creature token is "Unstable Shabti". You're right, now that it has two activated ability, the second ability seems too undercosted. The first is a bit undercosted too.

If that's the case, then your syntax needs to change. See Gild and Tolsimir Wolfblood: It has to read "Put a 3/1 red and white Shabti artifat creature token with haste named Unstable Shabti onto the battlefield." Otherwise, the game treats Unstable as a name and creature type for the token.