Question

I dont get it?

Answer 1

well rhydon and various other pokemon can use it if they have horns all it does it has 30% chance of hitting thats why it does one hit KO and 5 pp

Comments

unless they have STURDY.  then i think it fails no matter what

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also, it can't hit if your pokemon is lower level

Answer 2

Horn Drill and other 1 hit KO moves use... well this.

Type: Normal

Category: Physical

Power: -

Accuracy: -

PP: 5 (max. 8)

Introduced: Generation I

Targets a single adjacent Pokemon.

Effects

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)

Comments

A little advice: Please try not to answer old questions.

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At least others who click on this question will see my answer.

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Well, yeah, they will, but it's unnecessary. This answer is wrong anyway, if your Pokemon is even ONE level lower than your target, Horn Drill will fail. So, this is wrong. I would downvote, but this is your first time. Be careful with this stuff.

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I changed it. This time, I'm quoting from PDB. HA!