Campaign Mode strategy: There is practically no chance to fail this level or not get the 3-star rating unless you are not familiar with Tower Defense games and their usual mechanics. The first five levels of world 1 are dedicated to teach you the basics of the game, so failing them is not quite plausible.
Notes for taking the Legendary Mode: Legendary mode will usually put you on the last leg (last wave) of the same level map – with a finite amount of starting coins to test your wits on surviving the given challenge. Since you are just starting the game, it is more likely that you will spend your time defeating the first 10 campaign mode rather than trying to beat the legendary mode. The reason for this is that you should try to earn as much stars first in order to render passive upgrades on your towers, prior to taking up on these – rather hard to defeat legendary challenges. An example is upgrading your troops. There are three levels of upgrades for your troops. The first one requires 4 stars, which then makes your barracks recruit three soldiers instead of just two. The second upgrade requires an additional 5 stars, which then renders your troops with increased health. The last upgrade requires 6 additional stars, which renders an increased damage from your soldiers. In total, having to fully upgrade your troops requires at least 15 stars – equivalent to at least 5 levels with 3-star rating. Passive upgrades are also available for your archers, cannons, and your wizard tower. One more reason for tackling the normal campaign mode first is for you to at least gather stronger Heroes to help you defeat the legendary challenges more easily.
Legendary strategy: Upon beating all levels with a 3-star rating, it is possible to play a game with all passive upgrades maxed out to their fullest. Start off by build a wizard tower and a barracks at the converging point at the “y” section in the map. As the resources come, upgrade them and build another wizard tower. Place Fee and Bolton at the back of the troops and have Lancelot lead the front-lines. You’ll be done in a minute with this one.