Is it possible to get a Water Guardian phylactery?

[General_Metrac]

I started a new youtube series and I ran into the problem and I'd really appreciate and answer if you would help . I see it in NEI so I would assume that you could get their essence, however I am killing him and it has not filled up the phylactery. Anyone care to explain? and also if so, can someone be so kind to post a link or their knowledge of what mobs I can and can't Phylactery? Thanks for any answers, I will respond to anyone.

-General_Metrac

 

[elenoire]

you can't get boss mob phylactery without spawning it in creative which include guardians. Most mobs without boss health bar could be captured though. if you want strong mobs i'd recommends hellcows(it have high defense and attack value) or minoshroom(120 hp minibos) if twilight forrest installed