Fill a medium size pot with 2 quarts of water, beer, and Old Bay seasoning. Bring to a boil over high heat. Drop crab in, bring back to a boil, and cook for 12 minutes.
Remove crab from pot and let cool. Drain and rinse pot; return it to the stove. Pick as much meat as possible from the crab and place the discarded shells back into the pot; set meat aside. Add butter to the pot and cook on low for 1 hour, stirring occasionally.
Pour butter through a fine-mesh strainer into a medium bowl. Discard the shells. Add crab meat and the rest of the ingredients to the butter; mix well. Put in the refrigerator to cool until solidified.
To use, place shucked oysters on a hot grill and scoop 1 tablespoon of butter onto each oyster. When oysters begin to boil, remove from heat and serve.