Deviation of 3-3 invasion - how to live/kill?
In the deviated form, white can play at B18 and the corner will live or die as a ko, or it can end up in seki.  Even if black has more than enough ko threats to win the battle, it is unlikely ever worth it.

$$Wcm4 Continuation of deviation: Ko
$$ +---------------------------------------+
$$ | 7 . 3 6 5 . . . . . . . . . . . . . . |
$$ | 2 1 a X X O . . . . . . . . . . . . . |
$$ | . X X X O O . . . . . . . . . . . . . |
$$ | 4 X O O . . . . . , . . . . . , . . . |
$$ | O O O . O . . . . . . . . . . . . . . |
$$ | . X X X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |


The corner lives or dies depending on who wins the two stage ko; black's normal defense of playing 7 at a won't work due to a shortage of liberties.

Alternatively, if white does not have sufficient ko threats the whole corner could end up as a seki as follows:

$$Wcm4 Continuation of deviation: Seki
$$ +---------------------------------------+
$$ | 8 a 3 6 5 7 . . . . . . . . . . . . . |
$$ | 2 1 . X X O . . . . . . . . . . . . . |
$$ | . X X X O O . . . . . . . . . . . . . |
$$ | 4 X O O . . . . . , . . . . . , . . . |
$$ | O O O . O . . . . . . . . . . . . . . |
$$ | . X X X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |


Note that in this variation, black can choose to start the same ko by playing 11 at a instead.