Re: Best semi-carry..
WTF? Shadow Fiend? what are you people saying.The guy askes for support/ROAMING early game that can transform into a carry lateron. If you roam with a SF from lvl 1 then you need to quit DotA as soon as possible. That thing has insane lane-control and needs all the farm early game, after that, yes, around level 9 when you are maxed with Shadow Razes, maxed with +60 damage from souls, and have your ulti, then yes, he becomes the most dangerous hero on the map. Then he becomes the ultimate ganker/killer. NOT FROM START! Also Storm, wtf? He also needs the levels/farm before he becomes useful. He can become one of the best gankers once he hits level 6, but remember, he NEEDS that first. So NO, he can't roam early. Tinker also requires fast leveling to be lvl 8 as quick as possible to start ganking. Only he can be a bigger threat than SF at lvl 8-9 that has carry potential. Yeah a lvl 8 Lion/Rhasta is to be feared, but they are not lategame. Then ES is probably your best lvl 1 roamer, but he has no lategame.
For the guy that started this topic... Most people misunderstood your question(I hope), or I did. What I think you asked was: What hero can roam from the start(lvl 1), gank enemies in different lanes from lvl 1-8 and then transform into a lategame threat. Well the answer is Sven/Alch and then something like PotM/Veno/Venge, Although a roaming PotM isn't that bigga threat cause she can miss her arrow, also Veno and Venge is better suited to stay gankers/support throughout the game, but like most agility heroes, they can carry.
...Sven/Alch (I guess wind/slardar can also do that, but :/, rather farm with them)