Aside from this usage,
X + が/も + X + だから/なので/etc is a way to remind X as a reason for something. It roughly means "(as you know,) because of the (unusual) X". Examples:
Your second question is harder to explain, but it's basically a kind of joke called セルフツッコミ, a tsukkomi made against one's own boke. If you don't know boke and tsukkomi, please learn them first elsewhere, for example this and this.
So, in this paragraph, this blog author has been making fun of how useless Pembar was (Pembar could do almot nothing before he was killed). Then he made a boke sentence, "Penbar at least should have made Ryuk and the audience laugh by saying 'Watashi nippongo shaberemaseen'!" This may not seem funny to you (it's actually not particularly funny to me, either), but this is intended to be a silly statement, or a boke. Here, ワタシニホンゴワカリマセーン itself is recognized as a classic and cheesy Japanese boke said to get a laugh (google it if you're interested).
Then 狙ってどうする followed, which roughly means "What's the point of trying to do so (i.e., trying to make them laugh)?", and it's working as a self-tsukkomi, the act of correcting his own silly joke and getting another laugh. ～というツッコミは聞こえません ("I don't (want to) hear such a tsukkomi like ～") is a bit redundant, but basically he is pretending he said the previous sentence seriously. (Maybe it's like "no boke intended, just like how English speakers say "no pun intended" when a pun is intended.)