Arbor Elf

[Zachandstuff]

Can you tap arbor elf to untap a forest to tap that same forest for an extra mana for the same mana cost of 1 card?!  Phew...that's a big sentence

[Keyeto]

You may tap the forest untapped by {Arbor Elf} for an additional mana.

[Teysa karlov]

I do see why not

Tap forest. 
One green mana in mana pool,
Tap arbor elf, untap forest
Forest again,  now 2 green mana floating
to be used at anytime in the turn this happens,

[Gorzo]

If I'm understanding your question correctly, yes.

Say you have 1 forest and 1 {Arbor Elf} in play. You may tap the forest for mana, adding {G} to your mana pool. Then, you can tap the arbor elf to untap the same forest, and tap the forest for {G} again. You now have {G}{G} in your mana pool, and can cast a spell like {Strangleroot Geist} with it!

Just remember that mana empties your pool as phases and turns end/change, so you will have to use this mana before you change to the next phase or it will be wasted away!

RESOLVED

[Zachandstuff]

Thanks guys...my friend chase sucks...

[Teysa karlov]

Thank you garzo for correcting my little mistake,

[Trunksthemighty]

You can also use  {Arbor Elf} to untap a shock land with a forest in the land type. You could tap  {Temple Garden} to add 1 {g} then tap arbor elf to untap temple garden then tap temple garden again for {w}