When I play Guzma & Hala, can I discard the Stadium I searched for as one of the 2 cards discarded to search for the Tool and Special Energy?
If you want to do the second effect you have to discard 2 cards "when you play this card", that is before you search for the Stadium.
Source: Cosmic Eclipse FAQ (2019-10-18), TPCi Rules Team (2019-10-31)

Relevant cards

Note: All applicable cards may not be listed below.
SM12_193
SM12_193
SM12_229
SM12_229