@Adeeb You don't need to fight the Thunder 4 times. I made 40k in 3 times total, including the first time to complete the game. By upgrading your Loot, you get more points. So just max Loot, Attack (to live), and Attack Speed. ^^
I got a(n) A+ on hard! My score was 4101958 with a max combo of 357. I scored 259 perfects, 95 greats, and 3 goods. I got only 0 bads and 0 misses! I was playing on 5 speed and had 0 crazy options on. Great game, I like it! Play it here: http://www.thorgaming.com/games/3926/feel-the-beat.html