If the Runner is already tagged, Doomscroll will do 3 net damage (CF. Hydra). Even if untagged, it's still an $3/3s/“↳2” (with a 1 tag plus 1 net facecheck); and if they were to run through it unbroken twice (without detagging), they'd take 4 damage (1 then 3).

Blank subs (like an offline ↳ If the Runner has at least 2 tags, …) are mostly upside (taxing Bankhar or Physarum an extra card or credit), but could be downside too (like enabling Phoenix).