Can I use Cradily's "Selective Slime" Ability if my opponent's Active Pokemon is already Burned, Confused, and Poisoned?
No, you cannot. The only exception is if one of those is an "enhanced" Special Condition, such as Poisoned that places 2 damage counters instead of 1 during Pokemon Checkup.
Source: Stellar Crown FAQ; TPCi Rules Team (2024-09-12)

Relevant cards

Note: All applicable cards may not be listed below.
SV7_6
SV7_6