If you ask me, what killed BattleTech was that blasted cartoon - though it did provide the one line that made it truly memorable:
"If you say 'information is ammuntion' one more time, I'm going to put this axe somewhere uncomfortable!"
Uh, anyway... I think the 'Mech you're referring to is the Phoeinx Hawk - although I did not have the majority of BattleTech products, I don't recall ever coming across a transformable Dougram/Shadow Hawk ( when I first started playing BattleTech, I didn't have any of the Tech manuals and tried to build the Macross - or as I knew them then, Robotech - mecha with what I thought were the correct weapons. I couldn't work out why I couldn't have a Warhammer/Tomahawk with twin PPCs and twin LRM15s. I later found out that FASA couldn't do it, either...! )
I liked the Shadow Hawk. It could do a bit of everything...
One thing I do have a slight grudge against BT is that BattleTech has led to the adoption of the word "Mech" to describe a piloted robot. I much prefer "mecha" - I've described the difference before as being between a walking tank and a dynamic, rocket-boosted, robot ninja...
Another of the BT oddities are the Clan "second-line" Mechs that appeared in the 3050 manual. These were of Japanese origin, and I was once told the story behind their design, but I've forgotten exactly what it was. The images that appeared here don't seem to match up with those designs, so I wonder if they were specially commisioned or are in the full set of Japanese BT images...