Sonic The Hedgehog turns 23; all Android and iOS games on sale for $1 (sorry WP)
Sonic Dash also isn't in the deal, because that game is free anyway. If you want to get in on the other games, just choose which one you want, and the platform you want it on, and get your deal on!
Sonic The Hedgehog 4: Episode II THD (Google Play)
Sonic & SEGA All-Stars Racing (iTunes App Store)