If Gastly attacks with "Little Grudge" and on the next turn is KO'd by Blastoise-EX's "Rapid Spin" attack, does the Energy get discarded from Blastoise EX or from the Pokemon that replaces it? Neither?
Blastoise EX was the "attacking Pokemon", so it loses an energy.
Source: Evolutions FAQ (2016-11-03), TPCi Rules Team (2016-11-03)

Relevant cards

Note: All applicable cards may not be listed below.
XY12_21
XY12_47