Ok, that's a bit harder to explain.
Both secondary challenged (which are optional by the way, you don't have to fulfill them) require your hero to have a disable (stun, slow, etc).
One ability has to disable the opponent. This disable has to be invoked in a special way, that does not yet exists in DotA.
This means, the disable has to come into effect in a special way, that's not yet present in DotA. I listed the existing 'conditions' in the spoiler.
For example, Apparition's Cold Feet
would fit that requirement (if it wasn't yet in DotA). If you don't leave the AoE during the duration of the spell, you get stunned. No other disable in DotA has this property. (Some might argue, that Light Strike Array and Split Earth share it, but imo, no).
One ability has to disable the opponent. This disable has to be unique and not yet existing in DotA.
Means, the disable itself may not be used in DotA yet. Existing types of disables are also listed in the spoiler.
As types of disables are generally used on more than one hero, I will list a new one here (if you really wanted to use it in your hero, go on. It's not a new idea and I won't suspect you of 'stealing' it here).
For example, Mind Control
(meaning, the ability to control an enemy hero entirely with your commands) would fulfill this challenge.
I would, however, not recommend to use a Mind Control spell, as it's generally held for way too powerful for DotA.