You're very skilled, and this game is better than many other, non-pixelated games. Just goes to show that graphics don't matter. Well, in this case, pixelation made it even scarier! :D Well done
To find the Secret (???) Boss, turn of all switches in the Power Plant other than the ones indicated on the wall (so turn on II, III, VI, IX, and X, and turn off all the other ones). Hope this helps!
Number One Tip: try to max out protection, buff, and healing spells (especially for Natz and Anna) as soon as possible - they are essential to surviving tougher bosses. Also, spam holy spells - they are extremely powerful.
Here are some must-have tips for you gamers:
1) always use barracks in pairs. What this means is having 2 barrack towers stationed next to each other and rallying the troops to guard the exact same position. This provides an extra, tough layer of protection.
2) Near your barracks, always station Archer towers and upgrade them as soon as possible. Mage towers should be your next priority, followed by Artillery. Artillery is especially useful when facing giant hordes of enemies, since it targets multiple enemies at a considerably high damage. They are great to be positioned near barracks, since this is where enemies will be slowed down, allowing one to pound them with bombs.