Can I use Regidrago VSTAR's "Legacy Star" Ability if I have less than 7 cards remaining in my deck?
Yes, if you have less than 7 cards in your deck you must discard them all.
Source: TPCi Rules Team (2024-07-25)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH12_136
SWSH12_136