Mad Stan is the third character who originally appeared in the Batman Beyond Super Post, where I said:
Stanley Lebowski's first appearance was in the Batman Beyond episode "Rats" (1999). In comics, he first "appeared" in Batman Beyond [miniseries] #4 (November 2010), but it was actually just someone in a disguise. He was killed sometime previously.
What I should've said was seemingly killed sometime previously, because Mad Stan seems to have been mentioned again in Batman Beyond #1 (January 2011) before finally making his first appearance in Batman Beyond #3 (March 2012), where he was the focus of a whole story arc