As your problem is not strictly formulated, I can only suppose that the following code may be appropriate to your aim.
In[1]:= list = {2, 8, 9, 6, 3, 3, 9, 2, 4, 6, 10, 2, 1, 0, 3, 9, 3, 9,
7, 10};
list //. {a___, b_, c_, d___} /; Abs[b - c] <= 1 -> {a, d}
Out[2]= {2, 6, 9, 2, 4, 6, 10, 0, 3, 9, 3, 9, 7, 10}
