We made it on gold the last time we did it
I can't imagine doing alle the missions on advanced and silver them tho :S
Well, I did it. First attempt too, albeit I did lose a lot of lives. Getting silver on The Heliophage playing solo takes a degree of luck. It mainly comes down to whether or not you get the Varelsi Conservator as a boss during the boss rush section of the Rendain battle. If you get the Conservator, you can just farm extra score without killing it.
Thankfully, on Advanced mode, the boss rush sees fit to throw you TWO bosses at a time for three times. On Advanced mode, you are almost guaranteed to get the Conservator, on normal mode...maybe not.
Just Phoebe left to unlock. One command rank away from getting her, but...I'll wait until tomorrow.