From Sonic Retro
Orcas are aquatic mammals that appear in several 3D games in the series, often serving as a level element or background decoration to add to the liveliness of a setpiece. They are infamous for chasing Sonic the Hedgehog throughout mutliple scenes, usually in tropical environments.
Sonic the Hedgehog (2006)
An orca appears in Sonic 2006's Wave Ocean, and again chases Sonic across wooden platforms. Sonic hangs onto its dorsal fin and gets flung off when Tails closes the gate to keep the orca inside. This is also a call-back to the "Orca Chase" from Sonic Adventure.
In the Nintendo 3DS version, it appears in its original habitat in Emerald Coast for both Sonics. In Classic Sonic's Act, the orca chases Sonic on a 2D plane through an obstacle course full of crates and holes in the bridge, resulting in death if Sonic drops in. In Modern Sonic's Act, it appears at the end of the Act and is much more aggressive, thrusting Sonic into a Quick-time event in which the player must press three times to escape the orca. The orca also appears in Emerald Coast's entryway in White Space.
In the console/PC version, it appears in Seaside Hill, where orcas can either help Sonic by giving him a boost as to not to fall into the sea, or they are simply part of the environment when they jump, crossing each other. The orca also appears in Seaside Hill's entryway in White Space.
Sonic & All-Stars Racing and Sonic & All-Stars Racing Transformed
Orcas can be seen in the Seaside Hill tracks in Sonic & Sega All-Stars Racing as background props that don't interact with the racers. They also appear in Sonic & All-Stars Racing Transformed's Ocean View, jumping like in Seaside Hill, again not interacting with the racers.
Orca in Seaside Hill.
In Sonic Dash, the orca appears as a background element to serve as decoration once again.