what counters invoker mid ?

Best mid counters to Invoker:

1. Puck — strongest listed counter. Constantly punishes Invoker’s slow spell setup, dodges combos with Phase Shift, and controls teamfights with Coil.
2. Void Spirit — great gap-close and burst. Invoker struggles to kite him once he gets levels and disables.
3. Kez — high mobility and strong all-in potential; can overwhelm Invoker before he gets defensive items.

Also playable:

• Templar Assassin — especially good if you can pressure early and punish Invoker’s weak physical resistance.
• Lina or Storm Spirit can work, but they aren’t as strong in the provided matchup data.

Laning tip: don’t let Invoker freely farm with Forge Spirit/Alacrity. Contest ranged creeps, force out Cold Snap, and punish him when Tornado is on cooldown. Against Quas-Wex Invoker, avoid wasting your escape before Tornado/EMP.

For your pool, Puck or Void Spirit would be the cleanest answers—better than forcing OD into the matchup.

Source: STRATZ matchup data (7.41f reference).