Here is a solution using STUFF:
DECLARE @Heroes TABLE (
[Heroes_ID] int,
[Heroes_Name] NVARCHAR(20)
)
INSERT INTO @Heroes ( [Heroes_ID], [Heroes_Name] )
VALUES ( 1,'Superman' ), ( 2,'Batman' ), (3,'Ironman'), (4,'Wolverine')
SELECT * FROM @Heroes
SELECT STUFF((SELECT ', ' + [Heroes_Name]
FROM @Heroes
ORDER BY [Heroes_Name]
FOR XML PATH('')), 1, 1, '') AS [Output]