The Troll Hoard
Blades and Borrowed Things
Minikit #1 (Story Mode)
When you bring the gold chest down from the pile of junk, smash around in the rubble to find a minikit.
Minikit #2 (Free Play)
Use Saruman to blast away the Mithril bucket in the middle of the room--this creates some loose wraith bricks. Use Frodo's Ring to build these into a handle, then switch to a flail-user to yank down a minikit.
Minikit #3 (Free Play)
Use a Goblin character to climb up the net in the dark section of the zone. There's a minikit atop it.
Minikit #4 (Free Play)
Now use Saruman to blast away the Mithril door in the same area, revealing a minikit behind.
Minikit #5 (Story Mode)
There's a broken log to the left of the area. Bust up the grass covering it to grab the minikit inside.
Minikit #6 (Story Mode)
There are five sunflowers around the perimeter of the area. Blast them all with spells to earn another minikit.
The Hidden Pass
Minikit #7 (Story Mode)
While riding Radagast's sleigh, there will be five of these banners along the path. Smash into them all for a minikit.
Minikit #8 (Story Mode)
You'll see this along the path as your circle. Bear right to grab it.
Minikit #9 (Story Mode)
After busting through the rock wall, use Gandalf to enter the dark cave beyond and grab the exposed minikit.
Minikit #10 (Free Play)
Just beyond is a Mithril rock. Bust it up with Saruman's magic to reveal an action pad, then use a tinderbox character like Sam to light the nearby boards on fire. This will give you access to the slingshot targets behind--set the left to red, and the right to blue. This makes some Orc targets appear on the ledge above. Snipe these (two are beyond the large cracked rock wall) with an archer to spawn another minikit.