Does Drifblim's "Everyone Explode Now" attack count or do damage to the Drifloon that are underneath evolved Drifblim?
No, you only count the most evolved stage of a Pokemon in play. The previous stages are now part of that Pokemon.
Source: Stellar Crown FAQ; TPCi Rules Team (2024-09-12)

Relevant cards

Note: All applicable cards may not be listed below.
SV7_61
SV7_61