For those that aren’t interested in picking up physical or digital versions of the 2nd edition books just to convert a monster or two, you might want to check out the Forgotten Realms fandom wiki at http://forgottenrealms.fandom.com. They have a creature portal that looks to be quite extensive and each monster write up includes full descriptions, including backgrounds, histories, and ecologies as well as stats for at least 3rd edition and 5th edition, but some also have other editions like 4th, 2nd, and 1st laid out in a way that is easy to compare.
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