Den of the Bugbear is a rare Land card from Adventures in the Forgotten Realms (AFR), collector number 351. Current market price: $2.73 (foil $4.71), TCGplayer market prices via Scryfall.
If you control two or more other lands, this land enters tapped. {T}: Add {R}. {3}{R}: Until end of turn, this land becomes a 3/2 red Goblin creature with "Whenever this creature attacks, create a 1/1 red Goblin creature token that's tapped and attacking." It's still a land.