I got the drift badge on Stage 3 with Acceleration and Speed both at Rank 2. I went to the second lap and just did donuts banking off the walls in the bottom right. Finished with 9 seconds left and got 2200 drift points.
Sure assassins do more damage, but if you fully armor up your rank 1 soldiers, they become BEASTS with a maxed out block ability. I found myself simply not upgrading them at all and keeping my upgrades for archers and mages. 1 Tank per 6 creatures.. you don't need but a handful and they get attention long enough to kill'em. That and a rogue pairs nicely with but a single soldier flanking for him.
Either bat gang adds to your upward progress or the boost to bat game is to make it appear LESS. It's a huge hindrance at the end.
Also where the heck are the boosts to mines? To make them appear more often or boost you more?