The number of artifacts you control is checked only once: when Concussive Bolt resolves. If you don’t control three or more artifacts at that time, creatures will be able to block that turn, even if you gain control of more artifacts later in the turn.
2011-06-01
wotc
If you controlled three or more artifacts as Concussive Bolt resolved, the targeted player won’t be able to block with any creatures this turn. That is, the set of affected creatures isn’t locked in as the spell resolves.
2011-06-01
wotc
If the player is an illegal target when Concussive Bolt resolves, the spell won’t resolve. None of its effects will happen, even if you control three or more artifacts.
Format Legality
Standard
Not Legal
Future
Not Legal
Historic
Not Legal
Timeless
Not Legal
Gladiator
Not Legal
Pioneer
Not Legal
Modern
Legal
Legacy
Legal
Pauper
Legal
Vintage
Legal
Penny
Legal
Commander
Legal
Oathbreaker
Legal
Standardbrawl
Not Legal
Brawl
Not Legal
Alchemy
Not Legal
Paupercommander
Legal
Duel
Legal
Oldschool
Not Legal
Premodern
Not Legal
Predh
Legal
Who's Online
Live site activity across collectors, guests, and crawlers.