Io the Guardian Wisp is a highly unique ranged strength hero who works best as part of a communicative team. With its support-oriented skill set, Io is able to share its strength through Tether and Overcharge, harass enemy heroes out of the lane with Spirits, and materialize itself and an ally anywhere on the map with Relocate. Gank enemy Heroes, push undefended lanes, save teammates from deep within enemy territory - the possibilities are endless, and Io features one of the highest skill ceilings in the game.
 Recommended items
- Tether can be used on allied heroes to get to their side with great speed, as it latches from a considerable distance.
- Approaching a confrontation from behind will allow for easier use of Tether's slow. Positional items are also useful for this.
- Spirits requires much practice and focus to control, and due to its high mana cost it is not advisable to use it frivolously.
- Building Heart of Tarrasque or other HP regen items will allow for much more liberal use of your Overcharge. Also, the regen you get from these items will heal your tether partner, allowing you to heal allies by using Overcharge.
- Remember that Tether can be used on friendly creeps, and in a dangerous situation Io may be able to avoid death by Tethering to a lane creep, owing to Tether's large latch distance.
- Should an emergency arise, Io may Tether to a wounded ally and then Relocate to the fountain to heal both Io and his ally.
- You can also save the life of a crucial allied hero with this method, but it will often result in your own inevitable death when Relocate forces you to return to your original location. Be sure to un-Tether your ally before you return.
- The inverse of this can also work; Relocate from your fountain to the crucial ally and Tether them to bring them back. This is not always viable however, as it entails the 12 second discrepancy between Relocations.
- If Io's team has an end-game carry such as Phantom Assassin or Faceless Void, his top priority becomes ensuring the survival of this hero at any cost, including his own life. Io's skillset makes him very good at doing this, and if he succeeds in preserving the life of his carry then they will eventually become hugely powerful, and most likely win the game for their team.
- A good way to make Io cause a lot of damage with his nuke quickly is to summon the spirits, make them get closer, and when the cooldown has ended, get close to the enemy and activate the spell again. This way, all the spirits around you will explode damaging the enemy and five new ones will appear, potentially exploding on him too. Best used if Io is laning with someone with a good slow or stun, and when used to maximum potential (exploding all 10 spirits at maximum level) will cause 1000 magical damage.
- When ganking or escaping, always remember that Tether duration is the same as its cooldown, so it can be maintained on constantly as long as you have enough mana.
- Though using Tether to offer bonus healing from items such as Tranquil Boots or an Urn of Shadows charge is a good idea, your Tethered ally will not gain anything if you are fully healed. Using Overcharge to lower your health and mana before using any healing items will assure you are able to pass along the boosted regeneration.
- Soul Ring is an excellent Item if you have Tranquil Boots so that you can give your Tethered target HP regen and also the Soulring Activation Mana.
- A Bottle is good for the same reasons as Soul Ring; healing yourself and your partner in battle, and as well as giving mana.
- Mask of Madness is a great situational item for increasing Io's DPS and survivability. Thanks to Overcharge, at max level Io only takes 10% extra damage for up to 170 IAS, 30% extra movement speed and 20% lifesteal. Due to Io's fragility, however, it is important that Mask of Madness is used in conjunction with HP and Armour boosting Items, as he can't be burst damaged down while under its effects. Note that if you use Overcharge and Mask of Madness while tethered to an ally or Necro warrior/archer, the movement speed boost is increased to 47% for yourself, and the Tethered unit still gains the 20% damage reduction and 70 attack speed and 17% movement speed bonus.
 Io Partners
The most common playstyle for Io is to be partnered with a Carry, preferably one with mobility or health regen issues (as Io can help make up for both). Although any durability-focused carry can benefit from Io's support, among the better known Io Buddies are:
- Tiny, whose mobility issues are almost negated by the proper use of Relocate.
- Lifestealer, due to Infest allowing Relocate to take three heroes (including Io) instead of two.
- Chaos Knight, whose Reality Rift can bring an enemy into the Tether slow.
- Ursa, who benefits greatly by the mobility granted by Io.
- Riki, due to his ability to blink behind targets to trigger Tether slow while in Smoke Screen. The attack speed bonus from Overcharge synergizes extremely well with Backstab.
- Phantom Assassin, like Riki and Chaos Knight, can use her blink to trigger Tether's slow. Overcharge also synergizes very well with PA, making her more durable and allowing her to get more hits in.
- Slardar and Sven, both who have a terrifying presence with Relocate and can deal large amounts of damage in a short amount of time under the benefits of Overcharge.
- Legion Commander's heal is very powerful when combined with Tether. Io's Relocate can be used to Pick off lone enemies using Duel. Overcharge will increase the damage done during Duel and also reduce the damage taken during it. In addition, its very easy to hit all Spirits/Tether slow when the target is stuck in a duel.
- Io is the name of a priestess of Hera in Greek Mythology. She was seduced by Zeus and subsequently incurred Hera's wrath.
- Io is also the name of one of four Galilean moons of Jupiter, which was named after the same character in Greek Mythology.
- Wisp is the name of an Elemental from the Legend of Mana series, which has a similar appearance and is usually involved in healing.
- Io's fun names in DotA were Weird Ball and Santelmo. Santelmo may refer to St. Elmo's Fire, a weather phenomenon that creates sparks of bright energy similar to that of lightning, mostly occuring from sharply pointed structures.
- Enigma, Io, Keeper of the Light and Chaos Knight together represent the four fundamental forces of the universe with Io representing the strong nuclear force, as alluded to in his lore as the force that binds all matter together, as well as his abilities which mostly rely on being bound to a partner to achieve maximum effect.
- Oddly enough, Io is referred in the bio as "it", but the ingame description for Spirits says: "Io twists the particles of the universe with his unimaginable capabilities."
 Update history
- Fixed Tether sharing mana regeneration when you have full mana.
- Fixed Spirits initially spawning 250 units away instead of 150 units.
- Fixed the initial ability not being interrupted if Io was only disabled in the cast time but not when the teleportation happened.
- Fixed the initial ability not getting interrupted by Root debuffs ( Ensnare, Overgrowth, etc).
- Fixed ability not revealing fog of war for enemies.
- Fixed ability not showing the initial visual effect on the ground for enemies (only showed ping).
- Fixed being able to return Tether Relocate with a different set of targeting rules than the initial direction (no longer allowed to return relocate a creep).
- Fixed Overcharge missing a 2 second toggle cooldown.
- Fixed Tether sometimes ending prematurely if Relocate was cast before Tether.
- Fixed Relocated units sometimes walking away to do a previous behavior.
- Updated the textures for Death Prophet, Silencer, Drow Ranger, and Wisp.
- Updated the ability icons for Death Prophet, Silencer, and Wisp to match texture changes.
- Fixed being able to Teleport a Tethered creep to the enemy base.
- Fixed Chakra Magic mana regen not transfering over Tether.
- Fixed Spirits detonating on non-hero units like Spirit Bear.
- Fixed Spirits exploding on illusions.
- Fixed Relocate to not teleport Wisp while dead.
- Enabled Rubick, Wisp, and Luna in Captain's Mode.
- Fixed Magic Stick interaction with Tether.
- Overcharge and the two spirit control sub abilities no longer proc magic stick.
- Spirits no longer don't retain their vision after they explode.
- Fixed Relocate's return not interrupting other channeling spells (like TP Scroll).
- Fixed heroes continuing old movement orders after returning with Relocate.
- Fixed Soul Ring not working with Tether.
- Fixes for guardian spirits rendering with pops and such when entering/leaving FoW.
- Fixed Wisp voice lipsync getting stuck on with random noise.
- Fixed ranged display stomping on ambient effects, including Wisp.
- Fixed Tether being left behind when enemy teleported into FoW.
- Changed Guardian Wisp Explosion Effects.
- Added more obvious Wisp Tether Boundary Effect.
- Tether now shows the amount that it heals it's target.
- Wisp spirits no longer show up on the minimap.
- Wisp and his tethered unit move their camera when they Relocate and Relocate back.
- The Relocate sound stops correctly now.
 Balance changelog
- Tether now does a -100% MS/AS slow instead of a stun.
- Tether movement bonus decreased from 20% to 17%.
- Spirits no longer provide vision, except temporarily when they collide with an enemy hero.
- Overcharge hp/mp cost increased from 3.5% to 4.5%.
- Overcharge HP/MP cost over time increased from 2.5% to 3.5%.
- Tether regeneration transfer now heals the Tethered unit at 1.5x the rate of Wisp.
- Base damage increased from 33-42 to 43-52.
- Attack range increased from 525 to 575.
- Movement speed bonus reduced from 15/20/25/30% to 20%.
- Stun duration rebalanced from 1/1.25/1.5/1.75 to 0.75/1.25/1.75/2.25.
- Oscillation subabilities no longer interrupt Wisp's movement.
- Now circle slightly faster when there are fewer alive.
- No longer slow.
- Life duration increased by 3 seconds.
- Now spawn over 4 second interval instead of 6.
- Old Overcharge:
- Grants bonus attack speed, drains 2.5% of his current HP and MP per second. If Io is tethered to an ally the bonus attack speed is also granted to that ally.
- This is a toggle ability.
- Attack Speed: 60/80/100/120
- New Overcharge:
- Grants bonus attack speed and damage reduction, drains 2.5% of his current HP and MP per second. If Io is tethered to an ally attack speed and damage reduction is also granted to that ally.
- This is a toggle ability.
- Attack Speed: 40/50/60/70
- Damage Reduction: 5/10/15/20% [Reduces damage taken]
- Tether movement speed bonus reduced from 20/25/30/35 to 15/20/25/30.
- Spirits cooldown rescaled from 14 to 20/18/16/14.
- Tether Stun duration reduced from 1.25/1.5/1.75/2.0 to 1/1.25/1.5/1.75.
- Relocate cooldown increased from 80/60/40 to 90/75/60.
- Wisp can no longer teleport to the enemy fountain.
Alternate color theme, briefly used until the March 28, 2013 Patch
 See also