Invoker but, Quas, Wex, Exort abilities are actually the item slots: 'Z', 'X', 'C', 'V'.
so the hero has to buy active items and slot them to activate an instance of quas/wex/exort.
For example:
To unlock your first orb ability, you would probably rush Rusted Barrel.
Rusted Barrel would slot into the first item slot - when used it will grant you 1 orb instance 'Z'.
You can move your item in the different slots to activate different orbs, 'X', 'C', 'V'.
This design and idea opens up the 3 potential ability slots with 1 ability dedicated to invoke/the passive that enables this ability.
The 3 ability slots would probably be:
1 - consistent laning ability
2 - current invoked ability
3 - last invoked ability
Notes:
- Not sure if the hero has to activate and use the item or can just 'equip' it and 'unequip' it
- Not sure if this hero can use Blood tribute (Armlet item) to toggle orbs quickly.
- Not sure if this ability would be an ultimate and how Sinclar would steal/use this ultimate (but it would probably work normally)
- I think that the gameplay of item slot order management during shooting is fine - since a player may naturally do it in a real game after purchasing items/in general.