I applied online. The process took 2 months. I interviewed at Mercer in Oct 2015
Interview
Phone interview, where I was asked behavioural questions and things like when I could work and salary expectation, then an in person interview. The in person interview was a little more demanding, took a few hours and you meet with a bunch of different people. Some of the stuff they ask you overlaps with what previous people asked. But it's just to get a feel for your personality.
I applied through an employee referral. The process took 4 months. I interviewed at Mercer (Houston, TX) in Mar 2017
Interview
Video interview is the first stage. Be prepared for a mix of behavioral, industry, and problem solving. Phone call interview is the 2nd stage. Final stage is in house interview with 5 or 6 employees.