You know, I never once saw anything about back members popping up in Defense. I assume they appear when defending, but if they do, I don't know if the game tells you who helped out, and how much they contributed.

Anyone have confirmation on this?

Also, on upgrading idols: I think I read on the wiki that each upgrade version of an idol has her own base stats, and a bonus is given based on the two idols you combine.

Bonus is 5% of each idol's stats normally. An extra 5% is awarded for Max Level! (Actually haven't gotten anyone to max level myself, so I can't confirm yet.)

So, if I'm combining Rin A (ATK 400), and Rin B (ATK 800, Max Level), Rin+ will get 20 + 80 = 100 on top of her base Lv. 1 stats.

Hearts will combine, so if Rin A was at 10 Hearts and Rin B at 20, then Rin+ will have 30 Hearts.

Front members: If your Idol Assault Squad has a combined ATK Cost greater than your ATK stat, then some members won't be able to attend live stages, or will have their stats hampered.

For example, say you have 20 ATK, and you've got Yayoi (5), Iori (7), Yoko (7), Rin (2), and Donuts (5), from leader to 1st to last. That's...

Yayoi +5 (5), Iori +7 (12), Yoko +7 (19), and Rin +2 (21). Here, Rin is 1 point over your ATK, and so her stats are cut by 1 / 2 (the amount she exceeds your ATK, divided by her total Cost). Donuts... well, you're over your stat, so she sits back and eats dounuts.

Back members: When you've got more Stat than Cost in your unit, other idols will enter the fight. The game says they're chosen in order of cost-effectiveness (mathematically, Stat / Cost), but they'll only be able to throw out 80% of their total stat to help. Furthermore, if the last idol the game can fit in for you exceeds your Stat, then their effectiveness is cut much like the above (and they take a 20% hit as normal).

So... let's say you have 20 ATK, with: Yayoi (5), Mio (2), Uzuki (2), Rin (2), and Donuts (5). That's 16 Cost, so you've got 4 to spare.

First thing the game does, we'll say, is take your Yukari (3) and stick her in at 80%. You've got 1 Cost left.

So, the next idol the game gets for you is Donuts+ (I've seen this happen - send in the clones!), at 1000 ATK. She's 4 Cost over, so her stats are cut by 4 / 5 - she's got 200 ATK now. After that, she's sent in (without her donuts this time) at 80% effectiveness, netting you a total 160 to your ATK.

I'm presuming this happens on defense too, but as I said, if it does, the game isn't telling me who's jumping in for me. 'Least if it does, I don't know where it's telling me.