Sonic Frontiers' Combo Crackerjack achievement is a hard one to unlock, requiring you to activate Sonic's Phantom Rush ability by kicking and punching enemies a whole heap of times. The problem is that Sonic Frontiers' aggressive automations are quite easy to beat, and so getting the combos you need is a significant hurdle.
If you're just starting out, you might be confused as to how to unlock Sonic Frontiers fast travel (opens in new tab) system, or how to solve the Grave Mystery puzzle (opens in new tab) so you can leave the first island. Completionists may also want to grab the Egg Memo (opens in new tab) collectibles from each zone's Fishing Spot. Either way, here's how to get Phantom Rush and the best way to unlock Sonic Frontiers' Combo Crackerjack achievement.
How to get the Combo Crackerjack achievement
The requirement for the Combo Crackerjack achievement is to use the Phantom Rush ability 50 times in the open world which is pretty tough to complete. While it's easy to get Phantom Rush, since it's the second skill you unlock in the menu, it's much harder to use in practice as it requires you to max out your combo meter at 20 hits.
Essentially, once you punch enough stuff Phantom Rush will activate, letting you deal more damage and hit enemies with flurries of punches. The problem is that most enemies in Sonic Frontiers don't take many hits, meaning the only time you're likely to see Phantom Rush active is during Titan boss fights, since they can take lots of damage.
There is a way to farm up the achievement if you haven't beaten the Tower boss in the arena on the west side of the starting area, Kronos Island. During this boss, you have to kick and punch layers out of the Tower, which lets you build combo until Phantom Rush activates. Once active, you'll want to jump off the edge of the arena so that the Tower will respawn. It's very important that you don't beat the Tower, since it won't come back if you do.
If you plan to fight and defeat all of the Titan bosses, it might be better to just leave the Tower alive, and then see how many more Phantom Rushes you need to complete the achievement at the end. You can always go back and farm the remainder from the Tower if you really want to 100% the game.