9 max SnG 0.5$ hands A9o MP2

What is your question? Its always good to have a read on players who donk. If you think he likely has air on this dry board, I certainly understand the flop call. Still its a big flop bet and I might wait for a better spot without a read.

I don't really understand our river bet, is it a bluff or for value?

What could be done differently?
Difficult to say anything of his range in 1st hand indeed, KT+, QT+, small pairs, low and mid Aces, suited connectors + some other random hands.
Ofc A9 is a weak hand to open in the 1st hand (next time I fold ofc as SDK advised). Anyway, I think fold otf is best coz he may presume that A high will often call so it was reasonable of him value betting.
At that moment I thought he was bluffing and lets presume he really could have had bluffs. How do we drive him out most effectively and don't lose too much to value hands? Do we raise him otf and and give up to his further bets or if he checks all way long we bet big otr?

Redheater, I almost always post a separate post with the question)
I try to give a thought to a hand before I ask.

Pre-flop is indeed a close open, but not too bad I think.
As played it’s tricky to continue on a pot size bet on flop I think without any reads.
He could do it with a draw off course, but if the draw missed you most likely need to call a big turn bet as well.

The river I would check here. You beat some missed draws and it’s the question if you can fold a better hand here.

Cheers,
SDK1987

Ah, I didn't realize there was a second post coming. I will try to remember and wait a while next time!

Yes the open is marginal, according to the charts on here its a fold but a raise once the antes kick in. If the river is a bluff I can only think it is to fold out pocket pairs and better Ax, assuming these hands just flat called pre. About driving him out if he is bluffing - I don't think we need to. We have a bluff catcher of sorts so we can just call the flop as you did and try to get to showdown cheaply.