Off the scale
One of these two was never ranked, so this cannot move a ranking it is not in.
Nothing moves here either, and for the reason that governs the Franklin Richards pairing: the killer is off the scale by design. Tenth place rests on a toll counted in worlds over a span the setting measures in aeons, and characterised throughout as appetite rather than intent. One death in one branch of the future does not reach an argument built at that scale. This is also the thinnest citation the site accepts anywhere — `stated`, disclosed after the fact, never drawn — and it is worth reading against the Beyonders pages, where comparable entities die on the page.
The One Below All killed Galactus in The Immortal Hulk (2019).stated
revealed after the fact; the panel never shows it
Named as the inverse of the One Above All, dwelling at the base of the Below-Place.
In the far future it kills Franklin Richards, Galactus and Mister Immortal, until nothing else is left alive. — 2019
Possesses the Leader, who has stolen Banner's body, and is fought directly when it manifests.
The other end of the same being. It lives at the bottom of the Below-Place, it wants everything that exists to stop, and its route into this universe is the Hulk: every gamma death goes through its door and comes back wrong. It is up here rather than ranked because it almost never acts as itself — it works by possession. In one far-future timeline it wore the Hulk as the Breaker of Worlds and killed Franklin Richards, then Galactus, then everything else, because what it wants is to be alone.
Introduced preparing to consume Earth, with the worlds already eaten described rather than seen. — 1966
Given an origin as Galan of Taa, the sole survivor of a world killed by plague. — 1969
A planetary death toll accumulated steadily across billions of years, framed by the books as metabolism rather than malice. Enormously destructive and almost never in control of anything, including himself, which is a different problem from the ones ranked above him.
One death in one work. It is the only place the record puts these two in the same room, and it is evidence about that meeting and nothing wider — not a general matchup, not a rematch, and not a ranking of its own. The ladder above it is argued from everything either of them has been shown doing; this page is argued from one citation. Where the two disagree, the disagreement is the point, and it stays visible rather than being resolved by whichever of them happens to be on this page.
Both entries carry their full receipts on the Marvel ranking — 5 citations between them.