Speedrunners need practice saves. The official Binding of Isaac speedrunning leaderboards have a "Resources" section containing verified, virus-scanned 100% and Dead God saves. This is the source.
Once you have all characters, your job is to get for each of the 34 characters on Hard Mode. The hardest marks (and order of difficulty): binding of isaac repentance 100 save file
: Every character (including all Tainted versions), challenge, and secret is fully cleared. Speedrunners need practice saves
Right-click The Binding of Isaac in Steam > Properties > General. Toggle "Keep games saves in the Steam Cloud for The Binding of Isaac" to OFF . If you don't do this, Steam will overwrite your new 100% file with your old empty one. Once you have all characters, your job is
Some creators upload files with all items unlocked but no completion marks. This is a middle-ground for players who want to build crafting (Tainted Cain) but still beat bosses themselves.