How can I map BINARY(16) to GUID with Dapper?

If all your guid in our database are stored as BINARY(16) I would go on and create a Custom Type Handler to automatically convert the binary format to GUID. Something like:

class BinaryGuid {
  public Guid Guid;
  public BinaryGuid(byte[] binaryGuid) {
    <your-code-here>  
  } 
}

public class BinaryGuidHandler: SqlMapper.TypeHandler<BinaryGuid>
{
    public override Roles Parse(object value)
    {
        <your-code-here>
    }

    public override void SetValue(IDbDataParameter parameter, BinaryGuid value)
    {
        <your-code-here>
    }
}

then you register it for Dapper to use

SqlMapper.AddTypeHandler(new BinaryGuidHandler());

and you should be good to go:

var r = conn.Query<BinaryGuid>("SELECT MyBinaryGuid FROM MyTable")

I've written an article (and samples) on how to manage custom types in Dapper here:

https://medium.com/dapper-net/custom-type-handling-4b447b97c620