Shovel Knight: Treasure Trove

First off, I suggest going into options and switching your relic activation to Button mode so that you only have to tap to use relics rather than having to use the left thumbstick/d-pad and button combo. It makes the entire game much easier IMO.

There is a spot on the Pridemoor Keep stage that is fantastic for knocking out quite a few of these miscellaneous achievements. You'll reach a checkpoint with several of the flying enemies right at the checkpoint location. Using this spot, you can knock out multiple achievements. I suggest coming back after you've gotten all the relics so that you can use the Phase ability to group the enemies together better, then switch to the appropriate relic for each achievement. Leaving the checkpoint/enemies screen and re-entering it will respawn the enemies, and if you run out of magic you can simply commit suicide in the nearby pit to refill.

For Flying Feat, just lure the enemies together with Phase but don't get them too tightly grouped. You want them to be staggered with a couple higher and some others lower down toward the middle and bottom of the screen. Essentially you just want them all to start moving toward you but still be spread out. Jump up and activate your Propeller Dagger aiming for the top-most enemy. Keep spamming it as you fall and once you hit 3 enemies without touching the ground the achievement will unlock.

In the interest of creating as much of a one-stop-shop as possible, I've included 22 of the miscellaneous achievements in Shovel Knight in the video below. I wanted to include Knuckle Down as well, but the stage for that was already complete in my game and I haven't played back through again to unlock it. You can see Flying Feat at the 18:23 mark.

This achievement will require you to kill 3 enemies using the Propeller Dagger without touching the floor. Anywhere with 3+ enemies that would die in a single hit will work. I used this Hall in King Knight's stage. An easy area would probably be where all the Propeller Rats are in King Knight's stage i just didn't end up doing it there.

When you stab with the Dagger you're automatically lifted off the floor. Once you stab with it just know you need 3 enemies dead before your feet are allowed to touch the floor again.

Here is a video showing an area of where it can be done.