Works in TMCC mode with a Legacy also in TMCC mode.
I bought this to run behind a Lionel Legacy F7 (probably an F3 anyway), in a consist. In my Legacy PRR F7 AA set only the A lead unit is powered. I also have been pulling a Legacy SuperBass unit as well as 20+ cars - so powered A, unpowered B, and unpowered A. I wanted the extra power (it has two DC motors) for pulling more cars. I just lost two of 4 traction tires on the lead unit (after two years or so), so I think my need for more power is legit.
I contacted Lionel, who told me that the TMCC-equipped locomotive would not run in a "lash-up" with a Legacy unit.
But I run TMCC anyway, so my Legacy units are running in TMCC as well (not Legacy).
My new lash up is: Legacy powered "F7"- powered TMCC F3- unpowered Legacy Super Bass- Legacy F3 unpowered. Works fine!! Looks awesome!!