Happy Tree Friends Adventures

Happy Tree Friends Adventures is a fan game series created by radel999. It's mostly a crossover with Mario, sometimes Megaman.

So far, it has 6 sequels and a spinoff.

Gameplay
The objective of the games is to save HTF's world from Bowser's threat by rescuing the world's princess (Giggles in the first sequel). The game itself is a side-scrolling type with mainly enemies from Super Mario. Players can obtain gems for points, hearts for healing, and 1-UP items for extra life.

Happy Tree Friends Adventures
The objective of the game is to rescue Giggles from the hands of Bowser. Cuddles, Flaky, Petunia, and Nutty were the only playable characters. The game has some elements from Super Mario. It also contains bosses in certain levels.

Happy Tree Friends Adventures 2
This time, the objective of the game is to rescue the HTF's world princess. Giggles and Toothy are now added as playable characters. Each level is long and holds a boss.

Happy Tree Friends Adventures 3
It has the same objective as the previous sequel, but unlike the previous one the levels are shorter and bosses are only located in certain areas (the game has a map to show progress).

Happy Tree Friends Adventures 4
This game's mechanics have expanded this time. There are some levels that doesn't involve going on foot. Just like in the second sequel, each level is long and contains a boss at the end.

Happy Tree Friends Adventures 5
For this game, the tree friends' sprites are now different. But still, the objective remains the same. But instead of having difficult bosses in each level, Birdos are placed in almost every level's end. The main bosses are still located in certain levels though. More game mechanics are added, like the tree friends' ability to swim, climb, etc.

Happy Tree Friends Adventures 6
The tree friends' sprites are updated once more in this game. The game now has Megaman mechanics and enemies. Two extra characters are added, which are unlockable after you managed to access a certain event. The objective is still the same as well. However, more tree friends made their cameos, like Pop, Cub, Handy, Lumpy, and Flippy. There are also more villains like Lifty, Shifty, and Tiger General. As for the hidden characters, one is a fan character, while another one isn't from the HTF universe.

Happy Tree Friends Origins
This first spinoff doesn't star the 6 HTF characters as the playable characters. Instead, you have to play as one of two HTF fan characters. The objective of the game is to stop Bowser from summoning a deadly monster. Unlike the main games, this is the only game to show the characters being able to stomp on enemies to defeat them.