In order to use a catapult, you must pick up an explosive barrel with a Bricktron and load it in the catapult, then make the Bricktron operate the catapult. However, after loading an explosive barrel into a catapult, you can make the Bricktron pick up another barrel before operating the catapult. After firing the first barrel, the Bricktron will immediately load the second barrel in, allowing you to fire two barrels consecutively.
There is a fog of war in Castle Story that stops you from seeing enemies outside of your line of sight. Certain objects will dissipate the fog of war and give you vision away from your base. Bricktrons will let you see enemies around them, so you can use them to scout. Archers can see farther than Knights.
Also, captured crystals and shards will grant you vision around them.
Finally, lanterns are easy to build and can be camouflaged near hills and forests, granting you vision and warning you if enemies are approaching your base.
With a Bricktron selected, open the radial menu by holding right-click and select the "Jump Off" option to order the Bricktron to jump off a cliffside to the area you placed the order. This is particularly useful to quickly make archers jump off walls to escape enemies coming up the stairs, or to bypass an enemy's wall and jump into their base if there is a nearby cliff or mountain you can reach.
Besides with explosive barrels and catapults, it is possible to destroy enemies' walls with your units by selecting the Bricktron and opening the radial menu on the target brick, then selecting "dig voxel" or "destroy object".
Workers will destroy bricks much faster than Knights - it may be a viable strategy to sneak one or several Workers near an enemy's wall and destroy the lower bricks to poke a hole through their defenses!
Building beams on logs or brick plugs then lining planks on top of them is a great way to make ceilings, bridges or ramparts! It's possible to stretch your beams farther away (up to 10 beams!) by placing a brace under the first beam.
If using logs, place two logs on top of each other, a brace on the bottom one, then a long line of beams on the top one. The brace will allow the beam to be longer. The idea is the same with brick plugs.
Since it's recommended to stagger your walls, the brick patterns for archways and doors can be different.
For doors, start with 2 empty voxels;
Now, place the door, then place bricks on the second row, staggered, of course. This will leave 1 empty voxel on each side of the door.
Fill in the gap with half bricks and continue staggering in that fashion.
For Archways, start with 4 empty voxels on the first row of bricks.
Place two half bricks on either sides of the first row, then build a second row of bricks, starting on top of the two half-bricks.
Finally, place the square parts of the Arches on each empty space of the third row of bricks. Remember to stagger them!