Horn Drill and other 1 hit KO moves use... well this.
PP: 5 (max. 8)
Introduced: Generation I
Targets a single adjacent Pokemon.
If it hits, Horn Drill is guaranteed to make the opponent faint. It is more likely to hit Pokemon of a lower level than the user.
Its accuracy (as a percentage) is calculated as below, ignoring all other accuracy and evasion modifiers: UserLevel - TargetLevel + 30
This means that Horn Drill will fail against a target Pokemon at least 30 levels above the user.
In Generation I, Horn Drill had 30% accuracy, but did not affect opponents faster than the user.
Source:The Pokemon Database: Horn Drill (move)