Rosalina has the tools to exploit Sonic's main weaknesses: a linear approach and an inability to land. As per usual against Rosa, Sonic's goal is to remove Luma from the playing field, but Rosa can make this difficult for Sonic due to her large disjoints.
Rosa should be aiming to get Sonic in the air. Rosa is probably the hardest character to land against with Sonic because of the huge hitboxes and power of her Uair and Usmash. Her floaty nature can also pressure Sonic offstage as well, although his recovery is quite difficult to gimp. Getting Sonic in the corner is essential, because he can't exploit his movement and mixups.
What moves you use to keep Sonic out should be mixed up at all times. Every move you use can be punished by Sonic if he catches on to what you're doing. You like to use nair? We can run under and punish. Getting jab happy? We can Spin Charge under it. If you play reactionary you can make it difficult for Sonic to find your habits. Equally, you can punish Sonic for using the same approach options, its especially important to be aware of spin patterns since Sonic has multiple options when using the move, if he spin dashes your shield he is forced to use some kind of option to escape, which Rosa can punish easily.
Sonic's main methods of removing Luma include his jab combo, the SDJ and fthrow. With Luma gone Sonic can chase you down with his superior speed, making camping difficult. However, since our approach is somewhat limited to begin with, knocking Sonic away to stall time isn't too difficult.
Sonic's ability to KO is below average if he can't get hard reads. His kill moves include Bair, Usmash, Fsmash, Full charge Homing Attack, Fair and Uair near blastzones, Bthrow on the ledge. He can also use Uthrow, Fthrow and Nair at very high %. Since Rosa is so light he doesn't struggle so badly, but a patient Rosa is very difficult to land kill moves on. We can exploit Rosa's recovery like most characters, but we're hardly Villager tier edgeguarding so just mix up your recovery as always.
Take Sonic to Battlefield, Dreamland or Lylat. The platforms make it harder for Sonic to land. Town and City's low ceiling can also benefit your Uair. Avoid FD and Duck Hunt as they give Sonic more room to exploit his movement. If you dare to take Sonic to Omega Windy Hill prepare for the beating of a life time, the music gives Sonic mains their power.
General Stuff for Sonic
- Since Rosa has the worst standard ledge getup and a tall height, Sonic's Usmash covers this option very well.
- Uthrow>Upb>Uair is not a kill combo unless you get grabbed on a platform, in which it can kill as low as 60%.
- Our combos outside of Spin Dash are nothing special, if you avoid Spins you'll easily outdamage Sonic.
- Autocanceled Uair>UpB>Uair is a true combo that can kill at around 110%.
- Midair Spinshots use up our jump.
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