The visual effect of Oracle's Extract, with a faint circle to indicate the true sight range.
Notes
Oracle's Extract is automatically applied when purchased (even while dead) if there are already 6 items in the inventory.
The buff timer may look as though the player is being cheated out of Oracle's Extract duration by doing this, but this is only because the player's remaining death timer is added to the extract's duration. The actual time the extract is active once they respawn is unaffected.
The highlight from the detection radius only applies when a champion or trap is within the radius and not visible, such as standing in a bush, or being Nearsighted. Enemy units highlighted by the detection radius are not able to be targeted by abilities or basic attacks.
Strategy
The most obvious use for Oracle's Extract is to dispatch Stealthed Traps. This may cause the trap laying champion to be more trickier with their traps. Destroying enough traps can allow the Oracle's Extract to pay for itself.
Oracle's Extract can completely shutdown any enemy champion that uses Invisibility as a form of defense, making the champion super vulnerable. This mainly affects champions with the ability to go in and out of stealth multiple times, like Vayne or Akali, but can also be effective on champions that have one big stealth meant to avoid damage like Talon or Wukong.
Oracle's Extract has no effect on champions that use Camouflage, as when a champion with Oracle's Extract gets close enough that the extract would reveal the enemy, they are already close enough to see the enemy with the normal way camouflage works.
Counterplay
Even though the champion has an active Oracle's Extract, they can not remove any of the detected mushrooms without at least triggering one of them.
it is sometimes beneficial to force the enemy team to waste money to clear out your traps, place your traps on highly contested points like brushes or Health Relics.
If the enemy team invests in Oracle's Extract to diminish the trap's effectiveness, start using the traps actively in fights, or place the traps in brushes, causing the enemy team to spend more time on trying to remove the traps. Another option is to cover an entire brush with them so they can't remove them without activating at least one trap, see image to the right.
If playing as Teemo or Jhin, it's possible to save charges and place many traps all at once to overwork the people trying to remove them, leaving them open or preventing them from having enough time to remove all the traps.
If playing as a champion with Invisibility as a core mechanic:
realize that using the invisibility as a form of defense is not an option against enemies that buy Oracle's Extract.
Use any invisibility the champion may have in combination with brushes, disrupting the enemy.
It may be possible to focus the champion with the extract, but more than likely the tanks will have it, instead try to attack around the enemy with the extract, avoiding them.
If the champion normally uses the stealth as an initiation, like Talon or Qiyana, try to let an ally initiate, then come in behind them avoiding the aggro. That'll let their invisibility be used as a means of escape towards the end of the fight, instead of being wasted at the start.
