There's no doubting that this thing was pretty evil: it killed Tasha Yar and its main motivation was to sadistically torture the crew members stranded on Vagra II. It was immune to phaser fire, discharge energy blasts, generate energy fields that could block sensors and communicators and could change its shape. But it was also a walking oil slick. It was goop plain and simple - supposedly the left-over residue of all the negative emotions and vices of a race known only as the "titans". Remember them? No, apparently nobody did. Still, if you wanted to convey that this alien was supposed to represent the complete sum of an entire race's negativity, then don't you think it would be a little bit bigger than a walking outline of bubbling crude? It's obvious that this creature was incredibly powerful on a superhuman level, but it was near impossible to accept the package. Furthermore, it killed Tasha Yar in what had to be one of the most pointless deaths ever imagined for a cast member of a TV series - all she did was try to walk to the shuttle, for Q's sakes.