well you can't "require" ... "optional puzzles"
Anyways off the top of my head...
You could create mazes like in Canal
where you have to overcome obstacles with actions like burrowing and destroying "hinges"
You can have the player decode a message and choose the appropriate letters by killing units, dropping them (this may be useful for giving instructions in general as you can write paragraphs for units in dropships), etc.
You can have players solve musical puzzles by interacting with units (kill, attack, move to, move) that correspond to certain notes, to match a melody played to the user.
You can create riddles like the chicken, fox, and grain, where you have to carry them all across an area, and can only carry one across an area at a time (leave the chicken and the grain alone, and the chicken eats the grain, leave the fox and the chicken alone and the fox eats the chicken) using labeled powerups and a worker
You could implement something like minesweeper, if you pick the wrong space the mine gets given to an enemy computer and consequently kills or damages the player
You could have players "push" blocks using collision detection
& my handy movement math
You could simply take something from pretty much any part of a zelda game (keys (powerups), switches (kill units morph guards), using different items (spell selection systems like dropships), staying out of the sight of guards (use fog?), collecting hidden rupees (not visible, you have to walk into them))
Rs_yes-im4real - Clan Aura - helms.net16.netReached the top of StarCraft theory crafting 2:12 AM CST, August 2nd, 2014.