Defeating the Iron Challenge for Kingdom Rush Origins: Gray Ravens (Level 1)
Choosing the Iron Challenge
Once you've completed a level and earned three stars (this option doesn't exist until you've gotten three stars), you can now choose to do challenges on that level. The Iron Challenge option takes away some of your towers forcing you to only use two. You have to be careful with tower placement with these limited options. The challenges are a lot of fun, and, if you complete it, you earn an extra star that can be used for upgrades.
To choose the Iron Challenge, tap on the Gray Ravens level. Tap the small picture of the iron fist under the bar that says "Casual" as seen in the picture below.
When you start this level, a little warning will pop up telling you that you have limitations on towers you can use. There are also limits on tower upgrades. Even if you have upgraded your towers to the max, the upgrades won't show in the challenge.
For this level, you do not have access to archers or mage towers and there is a level 1 max on the tower upgrades. You have only one life (as opposed to the 20 you have on a normal level) and you will experience one big "super wave."
Placing Your First Towers
Because you only have the stone druids and barracks, you have to be careful about tower placement. Your money is limited and druids are expensive. I like to start by building a druid close to where the enemies come from. then I like to put up barracks right at the intersection of the two paths to catch enemies coming from either path. Keep an eye on your money to build additional towers as soon as possible.
Don't Forget to Use Your Reinforcements!
Reinforcements are crucial to beating these challenges. You'll want to add another barracks tower further down the path when you have the money, but you may have to rely on your reinforcements to keep enemies from slipping through until then. Also remember to use your hero and move him if needed. A good place to put him is right before the fork in the road so he can attack enemies from both paths.
When you complete the challenge without letting a single enemy through, you'll earn your extra star and some gems. This is why doing the challenges can help you beat harder levels later on. You'll get upgrades faster and have more gems to buy helpful items from the shop!
It's easy to keep track of the levels where you've already completed the iron challenge. They will turn from green to silver like in the picture below!