You've made a massive beater, but you need to hold it back for blocking if you want it to be most useful? That'll lead to boring stalemates and encourages bad gameplay.

Well, the flavour is very much "Doesn't attack much" so spot on hit there.

But yeah, for 7 mana you want something that'll actively win the game, not force you towards a stalemate.

The obvious solution? Give it vigilance, or something vigilance-alike. ": Untap ~" would be stupendous!

Also... not common. Not at all.

The not common part has more to do with NWO considerations than power-level ones. Even if this was a 3/3, it would discourage new players from attacking into it because a set full of cards like this would make combat too complex. Wizards tends to build sets using imaginary 'complexity points', however. So if the rest of your set isn't that complex, than one card like this shouldn't upset the entire cart.

This could also just replace the tap symbol with a mana cost. would do fine here. Or even or if you wanted to avoid players activating the card too many times in a turn.

This is basically Trolls of Tel-Jilad, which also wasn't common. For good reason: that thing dominates battlefields in limited.

Well it does cost 1 more, comes with 1 extra toughness and costs 1 less to activate.

Also, judging by the power creep since that set I think it fits.

This guy will be a bomb just not a very good one, much like a similar card, Kessig Dire Swine. Where this loses (possible) trample and a point of P&T you can sink mana in to regenerate something, allowing you to (in the late game) keep him and another creature on the board. Perhaps the cost should be then to solidify it as a mana sink and not a combat trick.

Basically, there's no way activated "Regenerate another target creature" is common under NWO.

Generally creature strength has trended upwards, but there's still a big difference between common and uncommon.

There are 3 effects close to this in standard right now, and they're all at uncommon and only can target attacking creatures (to encourage combat, not discourage it): Consul's Shieldguard, Nahiri's Machinations, and Ulrich's Kindred