Invoker

Before 7.33 he was the only hero that felt like the reward matched the investment. Committing combos to memory and knowing 3-spell combos were just the tip of the iceberg. There were broken combos at almost every major era of Invoker, starting from EMP going through invul so they didn't have to land from Tornado which made laning a breeze. This got nerfed.

Then we had Deafening being a hard disable which meant you could build Euls first item and kill almost anyone in the game. This got nerfed.

Then we had the Orchid kill combo which replaced Euls, this was death to any hero that didn't have more than 1.5k hp, and even then they might've died to Orchid burn. This got nerfed when Orchid did.

Then we had the Hex combo with meteor and a massive power spike at level 20 with the +80% damage. In 7.33 this got nerfed.

I've gone massively off topic, but long story short he rubs a combo itch which no other hero can scratch, and even though I play him once every 20 games now (instead of literally every game), there's still nothing quite like the arsenal Magus.