Enforcer Guild: "Find the evildoer harassing Darkwood!" -> On the way to Darkwood: "You have found the evildoer attacking Darkwood!" -> Attack: "You have defeated the evildoer attacking Darkwood!" -> Achievement: "No Dignity (Kill an enforcer party)"
How to finish the puzzles without ever listening to the musical cues: 1. Identify the largest piece. 2. Locate possible spots for the piece. 3. Put the piece into one of the possible spots. 4. Press Hint. 5. If it turns dark, go back to Step 3. If it stays lit, locate the next largest piece and go back to step 2 until all pieces are in place.
I beat -every- Cave with Viegraff, using only 2685 of his 'low' 2900 mana: Black Knight, Dragon Rider, Centaur Archer, Witch, Mermaid and Bomber for units, then Comet, Rain of Arrows, Phoenix, Lightning Bolt and Healing Wave. All Level 5. Patience and strategy works just as well. ;)
As for "Revenge Waves" coming too soon between each other - you might notice that their arrival is not actually based on time - it's actually based on the health of the enemy castle. That means, the faster you kill the castle, the faster the counter-attacks arrive. If you're feeling overwhelmed - then retreat your units the moment you hear the counter-attack signal-horn, to regroup and crush each wave one by one instead of all at once. Not every battle has to be won by brute force. ;)
Tips to reduce Smog in Challenges: Disable any Coal Power Plants you have, and never build any. For maps with Oil Wells, build Natural Gas Plants. For maps without, build Nuclear Plants. Build at least 2 Labs and make sure to upgrade your plants and vehicles. Also, to get a breakdown of your total smog production, click the Smog meter. You don't actually need a lot of farms, so build farms only when nearing a shortage.
Occult Rune (paraphrased for clarity): "Enchanted weapon will deal more damage depending on the target's defense. The greater the defense of the target, the more damage it deals."
You all serious? Not counting the three cards you get at the start, and the Yoshiro I got from the challenge, I've already gotten 11 cards from my 33 ranked matches. Maybe the chance of getting a card is higher if you beat a higher Skill Rank opponent, and lower if you beat a lower Skill Rank opponent? If not, then I'm now more uncertain of the actual chance to win a card than ever before.