BobTChicken

ISRO's Polar Satellite Launch Vehicle. Four stages, alternating solid and liquid. First and third stages are both HTPB, with the first stage filled with more than a hundred tons of boom. Second and fourth stages burn two *different* hypergolic liquids (UDMH/N2O4 and MMH/MON). First stage is augmented by six (count-em!) solid boosters, four of which ignite at launch and are dropped at T+ twenty-five seconds when the other two ignite. Totally amazing.

Since the Electron has electrically pumped engines, it could be cool to have a mod version that uses electrical charge while it's running.