Well if all its keeping track of is deaths then you could use a leaderboard, but if you really want a multiboard you simply make a variable like "NumberOfDeaths" and then you set up the multiboard.
And have it update the displayed value of "NumberOfDeaths" everytime someone dies, simply use Set Variable: "NumberOfDeaths = NumberOfDeaths + 1" Then "Multiboard - Set Item Text" and set it for the appropriate column and row and use the variable "NumberOfDeaths" and it will desplay the new value.
Sorry if its abit confusing, if you don't get it I suggest downloading a map that already has one and the maker is willing to share his code and looking at how the maker did it.