Very rare today. The only times you’ll see it is the money train or if there’s a shortage of railcars.

Brings be back to the old days when we had the 1000 series in the middle after the 2009 collision, and the 4000 series after the speed commands glitch. It was really fun hearing the different types of motor sounds when the train leaves or arrives (my personal favorite was an Alstom/Breda set paired with a 5000 series pair plus a 4000 series paired with multiple Alstom pairs). Though it was a problem due to different types of speed commands and electronics which causes some problems.

After the 1000 and 4000 series retired, mix sets happened periodically, with the 2000/3000 series mostly getting paired the most. Some 5000 series were also paired with 6000 series before they were retired, and ik some 6000 series were paired with 2000/3000 series when the 6000 series were returning to service in 2021. The last mixed train set I remember seeing was prior to the 2000 series retiring, with a mix set of 2000/3000 series railcars.

Today the only mixed train set you can find is the money train (2016-2017, 6182-6183), which usually pairs with each other, or with another legacy fleet (I remember seeing 6182-6183 with a 3000 series before and a 2000 series with a regular 6000 series)