Preflop
With two limpers in the pot you can go a bit bigger than 4BB, especially when you are this deep.
Flop
Standard C-bet.
Turn
His pot sized donk bet is a bit weird, and I think, the best play is to just call. You are fairly deep, so if you try to get stacks inside here, you might mostly get action from those few hands like A9 or JT, that beat you. Some reads would be nice here though, and the fishier he is, the more I want to raise this up and play for stacks.
River
As played a pretty trivial fold. Not only do you now lose to 9x, you also lose to any random Ax, and you are facing a big overbet jam. If I had to guess, I would say, that he probably had A9, K9 or Q9. It kind of makes sense, that a "fun" player would limp-call these hands preflop, check-call flop with one pair, make a pot sized donk bet on the turn with two pair and overbet jam the river with a boat.
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