How new are they, because it sounds like they're very new. If so, one would just direct them to written/video guides to learn some dota basics, instead of coaching them.
you could consider me very new, i have just logged around 300 games under my belt, i know for sure he is 80% done the all hero challenge, since we started dota and the all hero challenge around the same day. Ive only just played a few more games then him, and i do direct him to videos, its what he does before he plays any new hero to him. He told me yesterday that Mirana sucks, not the first time he's outright told me a character sucks, he said the same for just about half the heroes in the game. I cant force him to watch hour long match videos of people playing, though i do suggest it.
op/broken:
Meepo, if he dies, his timer is reduced in comparison, so late game he will have like a 60 second timer, while you are at 120. Kinda unfair honestly, considering he will just split push your whole base in, die, and buyback before you could ever respawn.
Void, what they said, and his evasion is annoying to deal with as well.
I wish Pa didnt crit so much, and i wish she didnt crit on her daggers, its kind of silly when she comes in and 3 shots or less every hero on your team.