1.Players joining the game are not harmed.
2.Monsters take damage(AI , Bot , NPC)
It is such a sword (recipe of ROBLOX)
https://www.roblox.com/library/47433/Sword?Category=Models&SortType=Relevance&SortAggregation=AllTime&CreatorId=1&Page=1&Position=2&SearchId=c9bff293-dd7f-4fde-a6d5-60c8b58252be
I cant exactly provide you with a fully scripted sword but it would be as simple as adding some sort of if statement to check if its not a player.
if not Player then
Damage()
end