Io build & guide (7.41)

Tether

Tethers Io to an allied unit, granting bonus movement speed to both. When Io restores health or mana, the tethered unit gains a portion of that amount. The tether breaks when the allied unit moves too far away, or Io cancels the tether. Tether slows enemies touching it.

Aghanim's Shard: Tether damages enemies touching it. Io is healed for 50% of the damage done.

Spirits

Summon five particle spirits that dance in a circle around Io. If a particle collides with an enemy hero, it explodes, damaging all enemy units in an area around it. Creeps take minor damage from touching a particle spirit, but do not cause them to explode. When its duration ends, any remaining Spirits explode.

Aghanim's Scepter: Spirits now passively spawn around Io constantly every second up to the max. Spirits colliding with enemy Heroes slows them briefly. Can be activated to explode spirits.

Overcharge

Io gains attack speed, spell amplification, and health regeneration based on max health. If Io is Tethered to an ally, that unit also gains any bonuses granted by Overcharge.

Spirits In

Sends the spirits closer to you. Can be toggled on and off.

Spirits Out

Sends the spirits farther away from you. Can be toggled on and off.

Relocate

Teleports Io and a tethered ally to any location. After the spell expires, Io and the tethered ally will return to their original location. Double-click to teleport to your team's base fountain.

Equilibrium

Io gains outgoing damage amplification the closer it is to full health, and Health Restoration and Healing Amplification the closer it is to zero health.