If I use Mega Sceptile EX's "Jagged Saber" attack against Giratina EX with the "Renegade Pulse" Ancient Trait, does Mega Sceptile EX's "Theta Stop" Ancient Trait prevent "Renegade Pulse" from blocking the damage? If not, then does "Renegade Pulse" prevent "Jagged Saber" from attaching any Grass Energy?
Renegade Pulse prevents all effects of attacks done to Giratina EX, but it does not "do anything" to Mega Sceptile EX for its Theta Stop to kick in. So the damage part is blocked by Renegade Pulse, but the effect of attaching energy is not being done to Giratina EX so that part of the attack does not get blocked.
Source: TPCi Rules Team (2015-09-03)

Relevant cards

Note: All applicable cards may not be listed below.
XY7_57
XY7_8
XY7_85
XY7_93