Epic typically runs a massive year-end sale (December) and a "Mega Sale" (May/June). During these events, Borderlands 2 GOTY has appeared as a surprise giveaway. You can also check SteamDB or r/FreeGameFindings on Reddit for alerts.
Every Thursday, the Epic Games Store gives away 1-2 free games. Borderlands 2 GOTY has appeared on this list twice. It will appear again. Make a habit of checking every Thursday morning. Borderlands 2 GOTY Free Game Download
If the deal isn't on Steam, Epic, GOG, or Humble Bundle, don't touch it. Epic typically runs a massive year-end sale (December)