Sentai has plenty of transforming trains
>Grand Liner (GoGo V)Cool robot but the trains really don't look like trains. The old DX toy is rare now but there is a SMP coming.
>Travelion (Magiranger)Cool locomotive but the robot has wonky proportions.
>ToQger lineA whole series about trains! Colorful train toys, ToQoh looks like shit because building robot out of vertical lines can only get you so far but good for train dick joke. Fun toys overall
>LupaPato X trainIs shit, don't bother
Transformers has the JRX from Car Robots (2000), great Shinkansen combiner for its time but super rare now and goes for ~20k yen nowadays
There is also Web Diver, which is only remembered for really really awful CGs and Tomokazu Sugita. The toys look great but hard to find now.
Shinkalion is part of the plarail line, great train toys but you are basically just buying the same robot over and over again. Get the following if you just want unique molds
>E5 Hayabusha>Doctor Yellow>DXS10 Trinity>E5 Hayabusha mk II>Alfa X>>7871347Super Robot Chogokin is straight action figures line, Soul of Chogokin and DX Chogokin are combining/transforming lines.