Sonic the Hedgehog 4: Episode II

Sonic the Hedgehog 4: Episode II is a video game in the Sonic the Hedgehog series. It takes place immedietly after the ending of Sonic the Hedgehog 4: Episode I and contains elements and call backs to Sonic CD.

Plot
Sonic, having defeated Dr. Eggman in Episode I, meets back up with Tails, who was secretly supporting Sonic's adventure in the previous title(such as building the rocket to allow Sonic to progress).

They discover Little Planet is returning, and decide to scout it out.

Dr. Eggman meanwhile locates and revives Metal Sonic, who had been badly damaged after the battle in Sonic the Hedgehog CD, and sends him after Sonic and Tails.

Gameplay
The gameplay remains very similar to Sonic the Hedgehog: Episode I with a few key differences.

Tails now accompanies Sonic on his adventure and can be controlled either via a second player or similar to Sonic the Hedgehog 2 where he follows Sonic behind essentially letting a single player play as both Sonic and Tails. Tails unfortunately cannot be played as the main character by a single player and likewise Sonic cannot be played solo.

There are new  'Tag Combo' combination attacks that can be performed with the press of a button, which are affected by the location in which the duo are when the button is pressed.


 * On the ground: Sonic and Tails will high five each other, and grab one anothers feet, transforming themselves into one giant devastating spindashing ball of destruction capable of breaking through stone.
 * In the air: Sonic and Tails high five and Tails will grab Sonic by the hand and fly him skywards, allowing him to reach places he otherwise wouldn't be able to.
 * Underwater: Sonic and Tails high five and Tails will grab Sonic and swim him to safety through hazards.

Additional changes from Episode I include:


 * Sonic no longer going in to free fall when launching off of ramps, instead continuing to stay in a ball if he launches up it in one.
 * Sonic no longer stopping dead in his tracks the moment the directional keys/pad aren't pressed.
 * The physics engine allowing Sonic to gain momentum whilst rolling down hill.

Special Stages are similar to Sonic the Hedgehog 2's halfpipe structure with Sonic and Tails both collecting enough rings to obtain a Chaos Emerald.

Obtaining all the Chaos Emeralds will allow Sonic to transform into Super Sonic on any act including boss battles providing he has 50 rings on his person. Over time his ring count will deplete. When he runs out of rings he reverts back to Super Sonic. Tails does not have access to his super form however.

Red Star Rings return from Sonic Colors and Sonic Generations. Collecting all of these will unlock an achievement/trophy.

Trivia

 * This is the first game since Sonic the Hedgehog 2006 that Tails has been a fully controllable character.