-Very weak lining phase, which usually is the opposite for int heroes.
-Relies on 'luck'... making the concept more unique but also, less reliable.
-Limited use in team fights (aoe slow is a big meh, single stun, if not multicasting, very limited)
-Limited into ganking early game (prior to level 11) due to INSANELY long cooldown on fireball compared to similar spells from other heroes.
All of these make him an tier 3 hero with a stun...
My ideas as to how to improve this hero... This hero is a ganker if you ask me... here's my idea of blacksmith:
-Fireball: needs to scale better in damage. I'd put it as 75,150,225,300 damage. Cooldown needs to be more in the 6 to 8 seconds right away at level 1 (no reason to be longer then Andro's stun).
-Slow: slows by 10,20,30,40%, deals 50, 100, 150, 200 damage.
-New spell: Burning speed (Passive): If not attacked for 10 seconds (no damage suffered, not from creeps, not from heroes), blacksmith gains a speed buff of 10,20,30,40%. This speed buff last until he gets hit.
Ultimate: Fireball can multicast the same, but instead of increasing the fireball price (right now, every time you increase the ult, fireball mana cost goes up), the blacksmith most 'pay' in mana every fireball he multi cast.
Ultimate: Slow stay the same, no need to make any modification.
Ultimate: Burning speed (Passive) adds 1 hit that must be received to remove the passive speed buff. If not attacked for 10 seconds, it recharges. (Pretty much, it adds a counter on blacksmith skill, at level 1 ultimate, he must be hit twice in 10 seconds to lose his speed buff. If he's hit once and not anymore, 10 seconds later, he regains the fact that he must be his twice before losing it). At level 3 ultimate, he would need to be hit 4 times before losing it... but if you really think about it, 4 times isn't much when creeps target you.
This would, I believe, buff him to fullfill his roll of a ganker. He will still have his small and crappy mana pool leaving him limited in that sens but hey.