In the Amber ink, a big archetype is having lots of characters out at once, so this should trigger nearly every time
The requirement of a damaged character to activate an ability that also requires you to exert her, alongside just 3 Willpower, Lady Tremaine is easily at the bottom of this list
They then have the option to perform several actions in their turn, in any order
If the target opponent is an illegal target as Tataru Taru's first ability tries to resolve, it won't resolve and none of its effects will happen
But dual ink cards are required to be played only in a deck using those two specific colors
If Gau is no longer on the battlefield when its last ability resolves, use its power as it last existed on the battlefield to determine how much damage the ability deals