Now for the fun Part; as of right now, the virus doesn't do anything, but this is where we change that...to do this, place a third command block with this command: effect give @e[tag=X] minecraft:blindness 600 5 This is just an example, but what it does is makes the infected unable to see in front of them...you can give any effect to them to customize the virus. Make sure this command block also repeats unconditionally and is always active. Have Fun!!!