Gaston Frightful Bullys Boost cost is a little high, but there are ways around that (see below)
The first is to counter all other spells, like a fancy Cancel that will normally counter one spell for three mana but here you can counter them all, which is good to end a stack war or storm effect
There are borderless, Through the Ages, and Surge Foil variants of each, upping the prices even further
Used at the right time, this can be a huge blow against an opponent who is strategically saving an action for maximum effect
If the second action is selected but no cards are selected for it, with no targets selected for the other actions either, then the effect is not added to the stack
For token decks, this means if one of your creatures produces a token when attacking, you get two instead