i was having an issue getting command block to apply effects to mobs but it randomly started working again as soon as i posted this... the command would give a positive output but the zombie would spawn with no effect and the same command worked in chat not in a command block. i think it was due to the fact that i was using more seconds in the command block than i was in chat. so typing a /effect ommand with 999999999 secs gives a positive output but no effect is actually applied