If I may be so bold as to help with some editing/grammar/spelling? Wonderful first work, and it's so amazing that you write so well when English is not your first language! English is not an easy language. I thought the plot was great, I only made some minor changes in spelling, grammar, and occasionally, some word choices to clarify what I thought you meant, and modified the format in a couple of places, also for clarity. As far as plot, I am hoping you would later clarify what this mage was attempting, and why it took him so many tries! He doesn't sound as competent as he seems to think he is. Suggestions and notes will be in green; changes in yellow. Sometimes I crossed out words, but sometimes I just left them out. Once I switched the order of two sentences, but there is no way I know of to make that notation from my keyboard. (Watch, now, probably Christopher Robin will know how...) Anyway, I did want to stress that you did a great job, the only ONLY reason I put in editing was because you said you wanted it. 🙂
It was pitch dark in the room and Dr. Holliday started to feel uneasy. It had been too long since he had heard from his associates. Disposing of a body can be dangerous; not an easy task for an amateur, but they had done it so many times that, for them, it was literally a walk in the park. But that idiot Sullivan hadn't checked in for 20 hours. The moron is a fucking cop, for God’s sake. What is taking so long? It is not the first time he has done it. Something must have happened... or that idiot forgot his phone again! Holliday fumed. Anyway, I have more pressing matters to attend to than getting frustrated. Like fixing THESE GODDAMNED RUNES. IT SHOULD HAVE WORKED...IT SHOULD HAVE WORKED! Dr Holliday could no longer control his rage, and angrily swept the documents from his desk. Sighing, he put his head on the desk and grabbed his hair with hands. Maybe tomorrow he could go through the university’s files and pick a new candidate. The candidate must have been tainted somehow, but he had checked and made sure that was not the case. Who knows? Maybe it was not to be this time. The FUCKING 62nd attempt. (Suggest adding more visible reaction, such as: Holliday's jaw clenched in anger.)
Notes: I decided which were Holliday's thoughts from context, and italicized them to show they are thoughts, not narrative. Then, because thoughts were italicized, I made the texts bold, to differentiate them, and added some identifiers to help the reader know if something was texted or thought.
A buzz broke the silence of the room, interrupting his thoughts. It was his phone. Then, the phone buzzed again. He finally gathered his strength and lifted his head. He took the phone from his pocket and opened his messages. The light from the phone illuminated his face, revealing a deep frowning lines on his aged face. There was a single sentence on that phone which quickly rekindled his rage.
I am cold.
Holliday immediately texted back, furiously: Idiot! What took you so long? Do you think that your job is the hard part? Try to translate the same DAMMED text again!
Holliday put the phone on his desk, but then it buzzed again. He checked his phone, sighing, and read the message.
Doctor, I am cold!
What is wrong with this idiot? I am in no mood for jokes, Holliday thought.
What are you? A CHILD? I am not in the mood for your stupid jokes!
The reply came shortly after that, and then another.
I AM SO COLD!
How are you feeling tonight, Doctor Holliday?
I have missed you. It was so dark down there and…
Mister policeman thinks so too.
An attachment was sent with the message. Holliday froze. He was feeling uneasy. He opened the attachment and a shiver ran over him. There was photo of Sullivan’s pale body impaled on a tree. And then another message came.
He is so cold and alone. Wouldn’t you like to join him?
There was another attachment sent this time. He opened the attachment. This time it was someone else. It was Jake. His body was on his bed, half dressed, pale and with his mouth open. His tongue and lips were white. His extremities showed frostbite. He looked like he had died from hypothermia. The area around his neck looked the strangest. It was purple, with marks that looked like fingers had left them. (My opinion: you do not need to say strangulation, the description is clear)
That was impossible. He has seen Jake on campus two hours ago. He glanced again at the picture. That resembled a campus bed. The killer was on campus! He started to panic. His counseling office was just 10 minutes away. Holliday felt like his stomach was churning. Who would be so stupid to attack them? He was a damned lieutenant in the Circle of Thorns, the biggest branch in Paragon City. He could crush any wannabe, inexperienced mage. Those idiots, Sullivan and Jake, were just weak initiates. And like the WEAK initiates they were, they died like flies. He is a paragon, a monster of the occult with knowledge amassed over thirty years within the Circle.
The phoned buzzed again, interrupting his attempts at a confidence boost.
Knock. Knock. Guess who is at the door?
The doorknob turned, and the door opened with a slow screech, allowing the light from the hallway to slowly penetrate into the room. Dr. Holliday froze in place. His newly rebuilt confidence just died (suggest withered, instead of died, More descriptive). It was like he was seeing a ghost. But the ritual failed, he thought to himself. NO! They checked the vitals.
“What’s the matter, Doctor?” asked a calm voice.
The air in the air chilled. Then the figure's right hand made a sudden move, and a frigid mist shot towards Holliday. (suggestion: a mist does not sound very threatening. Perhaps shards of ice? An icy blast?) He dodged that just in time, and then jumped out of the window into the courtyard of the University. There was not a single soul in sight. The night was chillier (suggest colder, as that is a stronger word than chillier) than usual. He turned towards the window and waited. Waited for the enemy to get out into his range of vision so he could attack with his spells. Nothing happened. Holliday strained all of his senses, searching the night for some sign of his enemy. Nothing was happening. The Circle mage saw a mist was forming in the courtyard. He could tell this wasn’t a spell of his enemy, but certainly had something to with his attacker, for it was not a natural phenomena for an autumn night. The mist was turning into a fog. His ears caught the sound of something to his left in the fog. He dodged again, just in time, as several ice bolts shot through the place where he had been standing earlier. He spoke a quick spell, and a bright wave appeared, pushing away the fog and objects within the area. But suddenly he realized his legs couldn't move, and they were so cold! He looked, and his legs were covered in thick layer of ice, as well as an area of about 6 or 7 seven meters around him. When had this happened? He realized the cold fog has done this to him, but now the fog had nearly dispersed. The ice began to spread from his feet upwards. He kept heating his body with fiery hands, but the ice was faster and he soon found himself covered in ice up the neck. His body was shivering uncontrollably. Hypothermia must be setting in, he thought. His teeth were now chattering.
And, that is all I have time for. Really should not have gone to bed before I even started this, sigh. For the rest, I'd suggest that you do not need to separate each of her lines of dialogue, since she is the only one speaking. Grammatically, they should not each be a separate line. If you want to break up the dialogue, to give some pause between lines of dialogue, you could write in some description of what she is doing, what he is doing, or something descriptive to add to the imagery. Most of the changes I made above were either spelling errors/omissions, or clarifying information. I rewrote three sentences because I felt that this was what you were trying to say, so I reworded it just a bit. Very good work, overall! And now I bet Christopher Robin has something to add. 🙂