These are the four games I had before and they are also on sale this Christmas:

Getting Over It with Bennett Foddy (2017) ($4, 50% off)
Undertale (2015) ($3, 70% off)
Battlevoid: Harbinger (2016) ($2, 80% off)
Particle Fleet: Emergence (2016) ($5, 67% off)

I'm adding four games:

Celeste (2018) ($5, 75% off) - platformer
Star Traders: 4X Empires (2014) ($5, 50% off) - light 4X sequel to Star Traders: Frontiers, mobile port.
Templar Battleforce (2015) ($5, 50% off) - turn-based tactical with 10-foot tall Mechs.
Hollow Knight (2017) ($7.50, 50% off) - sideview adventure game