Trainers » Guzma
Can I play Guzma if my opponent doesn't have any Pokemon on their Bench?
No, you cannot. If the opponent doesn't have a bench there's no way to do the second part of the trainer, and you cannot play a Trainer card for no effect.
Source: TPCi Rules Team (2017-08-31)

Relevant cards

Note: All applicable cards may not be listed below.
SM3_115
SM3_115a
SM3_115a
SM3_143
SMA_SV84
SMA_SV84