Google translate makes this sound like the person holding the cross and holy water is pretending to be an exorcist. An actual translation would be better, of course.
I'll pretend to be an exorcist. I'm an exorcist, so I'll do my duty on Koakuma. Hehehe
Okay, repeat after me: "Exorcizamus te, omnis immundus spiritus, omnis satanica potestas, omnis incursio infernalis adversarii, omnis legio, omnis congregatio et secta diabolica.
Ergo draco maledicte et omnis legio diabolica, adjuramus te, cessa decipere humanas creaturas, eisque aeternae Perditionis venenum propinare.
Vade Satana, inventor et magister omnis fallaciae, hostis humana salutis. Humiliare sub potenti manu Dei, contremisce et effuge, invocato a nobis sancto et terribli nomine, quem inferi tremunt.
Ab insidiis diaboli, libera nos Domine. Ut Ecclesium tuam secura tibi facias libertate servire, te rogamus audi nos. Ut inimicos sanctae Ecclesiae humiliare digneris, te rogamus, audi nos."
That's actually how you do it right. A part of the Roman Ritual, used by the catholic church in official exorcisms (yes, the church does that to this day).
... That was fun! ... Haha...
... Uh... You are just playing, right? ... Um, uh...(Tremble tremble) ... I'm not a bad devil!
I'm a good devil, one who loves you very much!
(Tremble tremble)