It's good when you can get it early, the game's going to go long and you aren't expecting to do much fighting in the near future. Carries are the ones that most commonly wind up in that position, but it's good on anyone given those specific circumstances.
Midas is one of those items that is better the earlier you get it. If you had an easy lane and can get one around the 5 minute mark, absolutely go for it. Anywhere after the 10 minute mark is pushing it, and will just slow down your core.
Since Midas gives you 30 attack speed, it's usually picked up by strong right clickers who can use the extra DPS, gold, and EXP. Carries like Naix, Skeleton King, and Void do well with this item. Other carries like Doom and Alchemist can pick it up if they're swimming in gold. Also it's pretty good on Nature's Prophet, since he can build it rather quickly, and it'll help him sneak in a few more hits on people trapped in his trees. I occasionally see this on invoker, but I'm not a big fan of that. On anyone else it's a little sketchy.
"...on a ps3 a realalistic looking megaman with a huge universe to explore rag dog physics." - Djmidnight1
I usually always get it on Furion and Naix since I can usually get it before 9 minutes on those heroes. It's a lot easier with prophet though since he's a really fast jungler and you're gonna get amazing GPM with that plus your pushing.
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