I am black at this game.
My biggest trouble at this game is that I am seeing white building a lot of influence, and I do not know what is the best way to reduce it. My "invasion" at left is bad (as it leads to the death of the lower left corner, very bad), and my invasion at bottom is also bad, as it leads to losing the lower right corner. However, I did that because I am worried that I will be sealed in by white -- although I was still sealed in at the end.
Some specific questions:
* W15 should be at G15 in the joseki, but I do not know what should I do to handle this deviation? Push through at F16 and then come back at E17?
* I was not sure where to play at B26. I ended up playing at M4 because I am thinking maybe I will be able to invade at H4 later -- of course, this invasion ended up getting me a lot of trouble.
* B28: my initial thought is to connect at D6, but then white will have very good influence and I'll be sealed in. So I tried to break through by D9... which ended up badly (because I lost corner while taking care of the left group.)
* B34: if I come back to the corner by playing at the position B4, would the left group die?
* I was surprised by the attachment at W53. How should I respond to that?
* I tried to reinforce the corner at B62. Would there be better choice?
* B64: I played there because I am worried that white would seal in that side. Unfortunately, that give white a shape point when he/she played at W67. What should I do here instead?
* B78: I think about cutting at O6, but it looks like that white can happily sacrifice some stone and seal me in. So I am not sure what I should do -- I ended up trying to play move to support an invasion at H4... and of course it didn't work out too well.
* B104 I thought about playing at L5 instead, but it seems that will put my bottom group at great danger. Is my assessment correct?
* B106: I want to do some reducing... and of course, my choice of move is bad again.
What should I play? * B120: If only the cut would work.... sigh.....
Btw, at what point of the game did I completely lose the advantage of the two handicap stones?
this shape feels a little funny.
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this exchange seems to help W.
This shape has problems, which W exploits immediately.
This is impossible. Tenuki is out of the question.
Your corner is dead shape. Huge loss, because of 
Very slow, almost a pass. You asked about the 2-stone handicap --
You should not have been surprised. You took high with 
--
Problem with this drop is you cannot resist when W turns with 
.
Lack of fighting spirit. Did you consider and read the double hane ?
Connect solidly is one option.
How many other variations did you read here.
How many other variations did you read here.
What's your plan here ? If you want to reduce W, just K5.
The local result here is the same as your 
-- it's almost a non-issue by comparison.
is connect at C15, that's joseki.
may be wrong -- I am wondering what I can do to limit white moyo, and I should have worried about that much earlier.
is also a decent move if you're worried about white making a big moyo at that point, though making the small knight's jump may be a bit more secure and has a nice followup of the two space jump up the left side if white tries to pressure the corner from the bottom. To be honest, though, I don't feel like white has spectacular potential in the center, as it's still quite open and black has strong groups to back up any reduction or invasion later.