There is literally no reason to ever not get Ygdar Orus Li Ox?

[Epic Store Exclusive]

So it seems if I expend it, I get to replace it with a new mutation anyway. As a result, this mutation doesn't really seem to have any actual cost.

Is there ever any reason why I would not want to choose it, since I get a free replacement if I use it?

[Scythia]

If you want the advantage given by a different mutation right away, instead of waiting to replace. Or, if you just want a little more challenge.

[bhoylhogro]

It won't work with cursed sword runs.

[Demonmax]

Besides, you start to get comfortable with the game, and end up choosing another mutation that may help you better early on.

This is specially noticed on higher difficulties, since it's more interesting to have CD reduction or one of the Curse mutations.

Cheers :)

[Ray G.]

If you're good enough to not die a silly death - then that's your reason. Also there's no point on taking it with you if you're on a cell farming run and don't care about finishing the game at that point. I find those mutation that lower the cooldown for either tactics skills or grenade skills extremely valueable early on - I take it first so I can shred through zones like a breeze without stopping, mostly because I always go for timed doors. I find those more valuable than YOLO mutation.

[Gem of Temporarity]

After it is used(and before replaced) then technically you're one mutation short. Possibly you wouldn't die if you had other one with yourself, but maybe you would and just saved yourself a regequit by picking YOLO.