'that so-and-so'; 'that thing', used to refer to someone in a rude way (to express one's dislike for a person) without referring to their name [colloquial]
A-chung just said he would use his most powerful move to knock out that monster in one hit. But his level was too low. The result was that not only did he fail to take down that monster, but he also ended up killed by the counter attack.