Retry is a free-to-play retro-styled one-button side-scrolling game developed by Rovio and is available for iOS and Android. The game seems to be heavily inspired by Flappy Bird in its styling, no-remorse difficulty, and controls. The goal of the game is to carefully control an airplane’s flight path from one hangar to another with the ultimate goal of getting to the final hangar in each stage. The tricky part is the difficulty of controlling the airplane without crashing into obstacles that litter the path. Holding the button will cause the plane to do loop-de-loops - tapping it just right will cause it to glide in a relatively straight line.
The most interesting thing about Retry is the way it utilizes habit formation to encourage (and perhaps trick) players to spending money on IAP.
IAP are are very discrete in Retry - at least in the early stages, which is when you want to be careful to not scare off potential paying users. Coins are primarily used to use checkpoints that are scattered throughout each level. So technically, a player is never forced to put money into the game but activating the checkpoints does make it a lot easier to progress through the levels.
The checkpoints can also be activated by watching a short full-screen video advertisement. Many checkpoints can be unlocked this way without any monetary cost to the player. There is a limit however to the number of checkpoints a player can unlock for free via ads. The number is large enough for the player to develop a habit - which starts a cue, is followed by the player’s routine, and finally completed with a reward (all reinforced by a neurological desire to complete this loop). Retry discretely reinforces the player’s craving for the reward by giving them many opportunities to unlock checkpoints for free. After the player is hooked, free checkpoints via video ads become disabled and only the option to unlock via spending coins remains.
Coins are extremely limited as you only earn coins by collecting them in each level (non-renewable) and from cashing in completed achievements. Since it is so important to unlock checkpoints in higher, more difficult levels the need for coins only increases with each completed stage. On the other end of the spectrum (the first dozen levels), coins are abundant and checkpoints are unnecessary to complete levels.
In addition to unlocking checkpoints, players may utilize power-ups, which require special silver coins, to help complete the more difficult levels.
The UI in Retry is very simple and typical of modern retro-styled pixel-art games; however, its simplicity allows users to easily and immediately distinguish different parts of the UI. Menu buttons are unified by the color yellow and are grouped up to the left edge of the screen. Most of the other buttons are also yellow - the exception being green play buttons.
The pause/current-level button remains on the screen in the top left corner at all times - during play and when viewing any part of the menu system - which makes it easy for the player to find the menu.
Player Retention (via Achievements)
Coins are awarded for all achievements but only if the player unlocks the achievement, visits the trophy menu, and clicks on the corresponding UI button - in contrast to traditional achievement systems that instantly reward the player as soon as the achievement condition is met. This simple design of forcing players to visit the trophy page increases the chances of getting them to browse the other achievement. Knowing that coins can be earned by completing achievements encourages players to seek those rewards and ultimately play the game longer. The achievements are designed in such a way that it mimicks a typical task-reward curve - that is, the first achievements are easy to obtain but as you unlocked more and more rewards, the achievement conditions become less trivial. This delayed reward system follows the difficulty curve of the game very well and only reinforces ‘good behavior’ (playing more) in players.
Posted by @LunarPeter