SBARG (partially found Homestuck ARG; 2012)
SBARG was a fan-made ARG for the webcomic Homestuck. It began September 25th, 2012 and lasted until October of that year. It was a massive deal on Tumblr, and the creator revealed that the official form for players had "14,033 individual entry submissions." Although most of the ARG's puzzles and content survive, the website where it hosted its Flash animations deleted them in 2015. One animation, "==> Enter" was rediscovered by the creator on MediaFire and can be downloaded here. The other found animation, "==> Ascend" was found on the Internet Archive and can be downloaded here, although misnamed.
The other four animations are lost. The creator admitted that the hard drive he originally stored the files on was "wiped clean to be used as an external storage device" in 2014. All that survives of them are these two stills:
References: Tumblr post by "onthisdateinhomestuck" talking about the ARG. Tumblr post on the official ARG blog, asking the community for assistance in locating the animations. Original page for the "==> Arrive on LoSaF" animation Original page for the "==> Strife!" animation Original page for the first "==>" animation Original page for the second "==>" animation Original page for the "==> Ascend" animation Original page for the "==> Enter" animation