non-standard tone pronunciation
There are three things going on here:


多 pronounced with a 2nd tone


If you observe carefully, you may notice that all examples of 多 with 2nd tone occur when the following character is 4th tone. I believe this is an erroneous extension of the same rule for the characters "一" (yī) and "不" (bù), which both become 2nd tone when the following character is 4th tone, such as the words "一定", "不够" etc. Standard Mandarin does not apply this rule for 多, but some dialects may.


複雜 as 3-2


Not sure about this one; may be a dialect thing.


Last character of word turned into 4th tone, e.g. 回來, 因爲


Actually the tone disappears instead of being 4th tone - it only sounds like 4th tone. It occurs when the last character is unstressed, it loses its tone and sometimes may have its vowel reduced too. Consider the following examples: 东西 dōngxi, 父亲 fùqin, 耳朵 ěrduo.

There are a few more rules covered in the Wikipedia article on Standard Chinese phonology.