While Goodra’s “Slimy Room” Ability is active, if I try to attach an Energy card but flip tails and have to discard my energy instead of attaching, can I try again?
Yes, as long as you can get another Energy card in your hand.
Source: Fusion Strike FAQ; TPCi Rules Team (2021-11-11)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH8_197
SWSH8_197