Credits:

YeahPotato

How To

NOTE: This setup uses the Rock Smash encounter table so it is recommended that you NOT use any rock smash boulders on the same map as your headbutt tree. It will not cause any problems but the encounters will be the same.

NOTE: It is recommended, although not required, that you set the encounter rate to 100 for maps using the headbutt tree. 

Script

Use a Signpost tile and set Kind: to Facing Any

Apply the following script to to the tiles

NOTE: All headbutt tree signpost tiles can share the same script address

section0:
  lockall
  checkattack Headbutt
  if.compare.goto varResult == 6 <section1>
  setanimation 0x800D
  bufferpartyPokemon buffer1 0x800D
  bufferattack buffer2 Headbutt
  msgbox.yesno <auto>
{
Something about this tree makes
you want to Headbutt it!

Should a Pokemon Headbutt it?
}
  closeonkeypress
  doanimation37
  waitstate
  special RockSmashWildEncounter
  releaseall
  end

section1:
  msgbox.sign <auto>
{
Something about this tree makes
you want to Headbutt it!
}
  releaseall
  end

section2:
  closeonkeypress
  releaseall
  end

This should, in theory, work in other games, however it has not been tested.

Happy Hacking!