What Sickly Does

Sickly is Max Stamina -25%, and by the game's own description the effect only applies to rideable Pals — it triggers while the Pal is out with you as your active partner, and stamina is the resource mounts spend on sprinting. It's the exact mirror of Fit as a Fiddle (+25%).

That makes Sickly the most ignorable negative passive in the game on the right Pal: base workers, ranch Pals, and anything you never ride are literally unaffected. On an actual mount it's severe — a quarter of the sprint bar gone — and worth fixing immediately.

How to Get Rid of It

Overwrite it at the Pal Surgery Table with any unlocked passive. On a mount, Fit as a Fiddle is a 10,000-gold default that turns -25% into +25% in one operation — a 50-point stamina swing. Sickly isn't on the surgery menu, so once overwritten it's gone for good; see the implants guide for the alternatives (on a non-mount, any positive passive beats a dead slot).