Looking through fighter archetypes and I see both the two-handed fighter archetype and the foehammer archetype have the Devastating Blow ability, which as a standard action threatens to critical every time. Since then I have found the wereboar rage power and the order of the warrior "strike true ability". Although the former is only with natural attack (no scythe fun) and the latter is only once per day.
What other classes have the ability to automatically threaten a critical?
Anyone with a cyclops helm, a cyclopean seer oracle with the flash of insight revelation (both 1/day), or anyone at all on a helpless opponent.
Indirectly, a druid summoning a cyclops.
11th level inspired blade using his inspired strike and 2 panache points (which he later on can regain).
Anyone with the ability to cast Named Bullet or use a wand of same.
Named Bullet
School divination; Level inquisitor 4, ranger 3, sorcerer/wizard 4, witch 4CASTING
Casting Time 1 standard action
Components V, S, M/DF (an item from the selected creature or creature type)EFFECT
Range touch
Target one piece of ammunition or one thrown weapon
Duration 10 minutes/level or until discharged
Saving Throw Will negates (harmless, object); Spell Resistance yes (harmless, object)DESCRIPTION
You imbue the target with deadly accuracy against a selected creature type (and subtype for humanoids or outsiders) or a specific creature you know and can name. When used against the selected creature, the ammunition never misfires and is unaffected by concealment (but not total concealment), and at a range of 30 feet or less, the attack targets the selected creature’s touch AC. When the target hits the selected creature, you must overcome that creature’s spell resistance, or this spell has no effect. A normal hit scored using the target against the selected creature is considered to be a critical threat and deals 1 extra point of damage per caster level (maximum 20), which is not multiplied on a critical hit. A natural critical hit deals the same extra damage, but that damage is multiplied due to the critical.
Once the target is used to attack the selected creature, successfully or not, this spell is discharged.