Super Street Fighter II Turbo (1994) was the first major fighting game developed for the Capcom Play System II (CPS2) arcade hardware, significantly upgrading the visuals and audio from the original CPS1 versions. 

Summary

• The “Turbo” Evolution: Following a period where the series slowed down in Super Street Fighter II, this version reintroduced faster gameplay with four selectable speed settings (and hidden faster speeds in some versions).
• Super Combo System: Introduced the Super Meter, allowing players to build energy by attacking and taking damage to unleash devastating, multi-hit “Super Combos”.
• Debut of Akuma: Introduced the first secret boss and hidden playable character, Akuma (Gouki in Japan), who kills M. Bison at the start of the final battle if specific requirements are met.
• “Old” Characters: Using secret codes, players can select “Old” versions of characters based on their Super Street Fighter II iterations, which lack Super Meters but often have different move properties. 

Gameplay Innovations

• Air Juggles: The first in the series to allow hitting opponents while they are airborne, enabling advanced combo sequences.
• Throw Softening: Introduced “Tech Hits,” allowing players to reduce damage from a throw by timing their own throw command.
• Refined Movesets: Every character received updated animations and at least one new special move or improved property for existing ones.