Submitted an application online during their general "Call for intern applications". I completed the initial set of questions, and also wrote out a few pages of theory on resource gating theory. The resource theory stuff was unsolicited - they said to feel free to add anything you felt would help you stand out, and I decided to go the extra mile to show how I thought about my work.
Next round of selections was a number of game-specific questionnaires. These were pretty standard, and you could tell there were expected right and wrong answers, but the emphasis was on explaining your thought process.
Follow-on to that was a phone interview. Scheduling for this was pretty straightforward. The interview itself was very informal, which seems to be somewhat par for the course when interacting with Riot. The interviewer tried to put me at ease, and overall I really enjoyed the process - I really wanted the job, but I felt like my thoughts put forward in the interview would be considered even if I wasn't given the job. It was a nice feeling- that even during the interview I was participating, instead of being "looked down at" as I had felt on other interviews.
When I was asked to come out for the on-site interview, Riot was very accommodating about making it a positive experience for me - I had asked about picking dates and times to fly so that I could attend the LCS super week that was happening, and not only could they accommodate the schedule I was looking at, they were able to get tickets for me after they had sold out.
They set up the intern interviews in a group and solo environment: There are a large number of interns interviewing each day, but only one for each position per day. This meant that you were not alone in being new, but there was no one there you were competing against for a spot.
Interviews were done by setting the candidate up in a room and then a number of project leads came to you and had the interviews there. I appreciated not having to move around a lot - it gave me some time and space to become comfortable with, and to put out my best foot forward.
All of the interviewers seemed interested in helping me to make my best impression - there were no questions that I felt were "trick questions" - they were all real questions designed to see if you could think creatively on your feet.
The interview with Mr. Cadwell was the most difficult - his questions were less directly game related than any other, and really challenged my ability to adapt quickly. There was a good 5 minutes where I thought he might be in the wrong room and was looking for someone with a more computer-science oriented background, since he was asking a lot about machine learning, which is something I have never really done.
I was asked back to participate in a second day of interviews, since they felt there were additional teams that I might be a good fit for. The second day was a bit more scattered, as there were still the standard intern interviews going on, and then my interviews were on top of this, but it was again a positive experience. I was able to meet with the additional teams and spent some time talking with them. Again, it felt like my input was valued even though I was just an interview candidate, and that made me feel more at ease during the process.
Riot seems to keep the interns with a single recruiter through the entire process, which made keeping track of whom to contact very easy.