Sonic Generations Playthrough 12: Planet Wisp Challenge
In order to pick up the key to open the Boss Gate, Sonic has to complete at least one Challenge Act in Planet Wisp, and this one has many different challenges, like combining powers, riding the cart to the goal, and help from Charmy in creating a path to the goal, and there is the boss fight for the Modern era, which should be the last one before we deal with that monster so that we can save the timelines.
As for the rest of the description, I recommend watching the full video before reading past this point of the description
Planet Wisp is the last stage in the Modern era, and one thing that I never went over is that its appearance in the original game makes it the first appearance of Planet Wisp outside of a Nintendo console, because the game it first appeared in, Sonic Colors, was only released on the Wii, it is on the DS as well, but the DS version had a different story to the Wii version.
With Your Powers Combined is the first Challenge Act for Planet Wisp, and this one combines Aqua Shield, Flame Shield, and Thunder Shield to get through parts of the stage and to get through certain hazards, then we get two Doppelganger Races in a row, first is Modern Sonic for Challenge 1 Act 2, and then after that is Classic Sonic's Doppelganger Race for Planet Wisp in Challenge 2 Act 1, but at least Planet Wisp has you making use of the Wisp powers, Orange Rocket for Modern Sonic, and Pink Spikes for Classic Sonic.
After that is Cart Challenge, and this one has you make use of the Carts, you can use a Homing Attack on the Egg Pawn to take the Cart and boost to go faster, and there are many Dash Rings you can go through.
Then for Classic Sonic, it is Goal Pole Juggle 2, this one seems easier than the one in Crisis City due to there being less enemies there, but you still have to watch out for them. Then after that is Charmy: High in the Sky, and for this one, Charmy can create whirlwinds which you can use as platforms, and you have to try to not get hit by the iron balls.
Challenge 4 starts with Chase After Blaze, and this one is a very quick one, all you have to do is catch Blaze before the time runs out, and Action Master is the next one, and this one has many obstacles and hazards, and it has you make use of various actions, like Light Speed Dash, Stomp, Wall Jump, grinding on rails, using Horizontal Bars, and many other kinds of actions.
Challenge 5 has the final challenges in the game, first up is Rescue the Animals 2, and this one, you have to rescue 100 animals trapped inside capsules, and you have to watch out for bombs dropped by Sprinklers, and then after that is Orange Rocket, Blast Off!, and for this one, you make use of the Orange Rocket Wisp Ability.
With all of the keys to the Boss Gate, our next opponent is the Egg Dragoon, which first appeared in Sonic Unleashed, and in that fight, you have to boost to attack the core, the Egg Dragoon changes how it attacks during the battle, and it has various attacks like a Drill Attack, Fire Beam, and Ice Waves, which you have to try and dodge. At some parts of the field, the battle shifts to 2D where you have to avoid its ice attack, and then it will attempt to trap Sonic using two walls, where you have to Wall Jump and then hit Eggman to deal damage.
In one 2D section of the fight, you have to get closer to the Egg Dragoon and attack it, then you go through a vertical tunnel where you have to boost to catch up and then hit the Egg Dragoon when you get closer.
Once the Egg Dragoon is down, we then get a cutscene where Tails decides to call a truce with Eggman, until the monster shows up and abducts him. Then we unlock the final Boss Gate, where we can take on that monster and restore time, and find out why the monster captured Eggman, as well as Classic Eggman back then.