The main issue with those abilities is that they would require a lot of infrastructure to be in place before being made (or a lot of specific triggering for just this one hero).
There is no simple way to figure out what a unit's attack damage is. You'd have to keep track of the items and various other things (such as buffs) that the unit has and then use that value for the attack damage. That is a lot of work to implement for just one hero, so having a system that does it for all the units is probably better, though it would also be a pain to set up.
Slowing casting time is almost infeasible. Though, it does spark some ideas in me for a casting system, which would be really cool, but also a ton of work.
% bonus damage debuff requires damage detection which involves another system. On the bright side, damage detection systems are already implemented in various forms allowing for a lot of freedom, but you would still have to get one into place and figure out how to use it.
If you are newer to triggers, I would go with easier solutions (you get a feel for what is easier after working with the editor a lot):
% bonus damage debuff -> armour reduction
Damage based on weapon / attack damage -> damage based on a hero attribute
Slower casting time -> silence
These aren't perfect translations, but if you haven't had much experience with the editor, these effects are a lot easier to create.