First the thread on damage calculation:
Second C-Rigard v Glenda:
Rigard boosts the attack of a hero. If a hero has 100 attack and special skill with 100% damage: that’s 100 “attack power”. Add in Rigard’s 48% boost and it’s 148.
Glenda boosts the special skill percentage. So instead of dealing 100% damage, she’ll buff it to 140% damage. Aka 140.
Now compare it if the hero does 500% damage.
100 base attack * 500% special skill = 500
100 base attack * 500% special skill * 1.48 attack boost = 740
100 base attack * (500% special skill + 40% buff) = 540
You can play around with the numbers in the example to get closer to what you’re looking for. Also this is just the attack part that gets put in the formula to the post I linked above and quoted below.