Kingdom Rush: Frontiers

This can be a tricky one. The hint says: "Apply one Falconeer bonus to 4 towers." This means you need to upgrade four of your Archer Towers to Crossbow Forts. Each Crossbow Fort needs to be next to another tower of any kind. After all your towers are placed and upgraded, add the Falconeer bonus to each of your four Crossbow Forts. This will give the Crossbow Forts and adjacent towers a purple ring around them. You will unlock the achievement once all eight of your towers have a purple ring.

You can "help Indiana find the secret passage" on stage 11 Temple of Sagra. Indiana will appear on the roof of the right hand side building. Quickly push the tiles on the wall in this order: Second tile, First tile, then Third tile. This will open the secret passage and crush the bed of Parasyte eggs. Don't mess up the order of the tiles, or you will release the little facehuggers, and no one wants to deal with them.

The "One Froggy Evening" achievement can be earned by catching the frog on level 3, "Sape Oasis". He will appear near the rock by the oasis on the top right side of the screen. Just click him when he pops up to make him sing, and you will earn the achievement.

The mermaid can be found in the fifth world "Buccaneer's Den". She doesn't pop up frequently, so you'll want to earn this is achievement after you've defeated all three levels (Campaign, Heroic Challenge, Iron Challenge). Keep your eye on the left hand side of the screen, she pops up under the boat near its anchor. Quickly click her to earn the achievement.