Sonic 2017's Official Title is Sonic Forces, Sonic Mania Delayed to Summer

SEGA announced a pair of updates regarding the two Sonic the Hedgehog games the publisher has in development.
The first gameplay of modern Sonic in Sonic Forces is coming soon.

SONIC MANIA Delayed Until Summer 2017 — GameTyrant

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Sonic Forces Announced Plus Sonic Mania Delayed –

Sonic Mania' delayed, 'Project Sonic 2017' is called 'Sonic Forces

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Sonic Mania delayed