Steady Foot
Can not be upgraded.
"Negative stat changes" does not just mean main stats.
The relics Steady Foot impacts are the following (parentheses will explain impact when not immediately clear):
Shell Cluster (Grants immunity to spread decrease not damage variance on bullets)
Fake Bill (Never receive curses when buying from shops. Since Fake Bill's effect is applied continuously this combo works even when receiving Steady Foot second)
Heart Locket (Never lose hp when opening doors without keys. Since Heart Locket's effect is applied continuously this combo works even when receiving Steady Foot second)
Bugspray (Fully negates damage multiplier. Since Bugspray's effect is applied continuously this combo works even when receiving Steady Foot second)
Moon Locket (Never receive curses when opening doors without keys. Since Moon Locket's effect is applied continuously this combo works even when receiving Steady Foot second)
Tesla Coil (This is an anti-synergy in regards to damage output however it could be useful if you value high shotspeed even with Tesla Coil)
Chaos (Never lose the relic upon entering a new floor. Since Chaos's effect is applied continuously this combo works even when receiving Steady Foot second)
Dust Bunny (Removes damage falloff. Since Dust Bunny's effect is applied continuously this combo works even when receiving Steady Foot second)
Leaking Battery
Phaser
Necronomicon (Never die upon hit)
Burst Clip (Negates the 40% fire rate down despite not being included in description)
Black Hole (This is a major anti-synergy in regards to damage output however it technically negates Black Hole's fire rate down as well as its shotspeed down)