I first saw this comic book cover back in the late '90s, when Comic Con was still lots of fun, though it was trending toward obnoxious media-con-ism by then big time. Had to have been after the Austin Powers movie came out, which was '97. I remembered it because at the time I thought it was hilarious, due to the word "shag" having been introduced to a mass US audience then. I wondered why Marvel never reproduced the story at the time, though I think it's probably not very expensive to find a readable copy of it.
I'd like to read it, as I have a fondness for those early Mavel/Atlas monster books, thanks in large to the reprints they did in the 70s. Turns out Shagg is a robot in the form of a sphynx and doesn't appear to be the brightest invader, though the story is left open ended and would be ripe for a sequel. Now I wonder how John Byrne never brought Shagg back, seems that would be right up his alley (with Spragg and Xemnu showing up in the She-Hulk book years ago).
It also turns out a M/NM copy sold for $148 a while ago, but I do think a readable copy would cheaper to purchase.