Admin commands help?

Tab your code properly.

It makes it easier to read and completely eliminates these errors.

Here is your code:

function Text(text,time,par,Texttype)
	local m=Instance.new(Texttype)
	m.Parent=par
	m.Text=text
	wait(time)
	if m~=nil then
		m:Destroy()
	end
end

game.Players.PlayerAdded:connect(function(plr)
	for i,v in pairs(Replicants)do
		if plr.Name:lower()==v:lower()then
			plr.Chatted:connect(
				function(msg)
					if msg:lower()=="@m" or msg:lower() == "@message" then
						Text("This is a message!",4,workspace,"Message")
					end -- REMOVE ME
					elseif msg:lower():sub(1,9)=="@m/"or "@message/" then
						Text(plr.Name..": "..msg:sub(4),4,workspace,"Message")
					end
				end
			)
		end
	end
end)

Notice yoru elseif. It is not attached to any if because the previous one was already ended.

Remove the end immediately before it and it should work fine.