I really don't have a clue what is "the right" play in this spot. Maybe it is not so important but anyway....

My reads are:
- 3x pf default
- calls pfr w Q8o and chks to RVR OOP on 5TKtt 2 A
- pfr, chk flop and calls turn bet chks rvr w KJo on 29Q Q A
- calls CB on 56Qr chk/chk turn 4s and bets rvr Ts 80-200 bringing BDF on bord w 55

so the hand:
This was my first 3B. I didn't bet flop because I saw him chk to rvr - he wasn't agro till this point. I bet turn because I don't wanna give any more free cards to BDF and overs (maybe I should bet bigger) and my EQ is MAYBE getting little better because i have 4new outs for str8. RVR i chk because I think that he'll bet smalish with good hands ( as he did with 55) and chk back his Ax with showdown value. But now he shoves like WTF ???

bet flop, bet turn, bet/fold river. I'm not a HU specialist.

With 10-20% pot size bets? -,^

As played just c-bet, and probably gii on this turn

As played I rather fold the river, I'd play around a bit with equilab/stove though.

your right duh...

I wasn't paying attention to his pre-flop 3 bet.

I like your call.

^^^This.

I've read OP three times and still don't understand logic of checking flop. Were you hoping to just check it down and, if so, why 3b it in the first place? Just wondering if I am missing something ... I mean, aside from hitting set this is about the best flop you could hope for when he flats the 3b.

This is the question I have to answer, but I don't have clear answer.
He opened 80% of BTNs (small sample - 25ish hands). At the time I just wanna to see how will he react to 3B. OTF I had SDV, If i bet nth worse doesn't pay me off and if he raises i have to fold ( because hi didn't show any agg postflop yet, and he didn't do any bluffs until now, everything was str8forward). When he called turn bet I was thinking there is some AX strong holdings and he was to stubborn to fold.
But then river didn't make any sense to me (at that point). As I said he would try to bet( in my oppinion) sth like 1/3 of the pot with good hands, and if he had AK or AJ, he would just chek behind, because he was so str8forward till now.

Now that I look back, I see that it would be better to CB flop and GII OTT, and as I played I would have to fold river.
Thanks for the answers !

I'll give this a sick one week bump because the rationale of including mid PPs in your 3b range is intersting to me. Hopefully one of the better players will jump in and give me an informative smack down where my thinking is off.

I think a lot of people will tell you not to 3b mid PPs deep (i.e., non-AI 3b's) because they are hard to play post-flop when you get called. Most flops will have overcards and now you are playing OOP with a bloated pot. I like to have them in my 3b range against villains who don't like fold pre but play fairly straight forward post. If he's going to call a lot of pretty looking hands but tend to be fit-fold post we hope to get a flop fold out of him 2/3 of the time and make some money on a hand that can be hard to play OOP. But make no mistake that's our goal ... a fold flop is a great result here. If you are going to 3b hands like 77-99 you aren't looking for worse hands to pay you off post-flop unless you hit your set and 3betting to set mine is god awful.

Of course, if villain is calling 3b's pre and playing fit-fold, we could better exploit him by 3betting our junk hands ... now we're getting value from an otherwise worthless hand. TBH, there are only three reasons I can think of for 3betting 88 instead of junk:
1 - I am pretty happy getting it in pre with 88 and I hate 3b folding at typical HUSNG stack depths.
2 - We can flop a monster and against this type of player, we are likely to get his stack when he connects.
3 - I prefer to take initiative with these hands instead of trying to play them OOP without initiative (esp against anyone with a high cbet %)

FWIW, the other situation where I like including mid PPs in my 3bet range is when villain gets really spewy when faced with significant aggression. Including these hands let's you create a wider value heavy 3b range.