The Drive-By Updater makes one, maybe two, edits and then disappears into oblivion. In many cases, this is a passing browser who spots an obvious mistake to fix. Also may exhibit the behavior of a Clueless Contributor.
There is nothing inherently wrong with Drive-By Updaters, but only if their contributions properly follow guidelines. Since most Drive-By Updaters don't bother to stick around to learn what those guidelines are, however, the practice can be less of a joy for the regular Tropers.
After The Google Incident anonymous edits were disabled, effectively making these contributors extinct on this wiki.
Compare and contrast Hit-and-Run Poster.