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Quantum Conundrum: Season Pass is on sale for $3.99 (75% off) at GMG. Use the voucher code GMG25-1BW0K-K1A3G to save an additional 25% off, which makes the DLC only $3.75.
Requires Steam and the base Quantum Conundrum game.
Actually it comes with the base game so only Steam is required.
Oh nice. Thanks for letting us know!