Prova a dirglielo così.
Il 2/2 attacca, passate alla fase di dichiarazione dei bloccanti. All'inizio di questa fase, prima che i giocatori ottengano la priorità, tu dichiari con chi vuoi bloccare chi, poi ottiene la priorità il giocatore di turno. In questo caso la situazione sarà: 2/2 attaccante con mishra's factory 2/2 assegnata come bloccante.Priorità al tuo avversario.Prima di passare all'assegnazione dei danni la priorità torna a te, per cui avrai l'opportunità di usare l'abilità attivata per dare alla mishra +1/+1.
Il fatto che la mishra sia tappata dopo la dichiarazione dei bloccanti non conta, perchè, come da regole citate qua sotto " Each chosen creature still controlled by the defending player becomes a blocking creature. Each one is blocking the attacking creatures chosen for it. It remains a blocking creature untilit’s removed from combat or the combat phase ends, whichever comes first", la creatura rimane bloccante a meno che 1)sia rimossa dal combattimento 2) Finisca la combat phase.
Dalle comprehensive rules:
Cita:
509.1g Each chosen creature still controlled by the defending player becomes a blocking creature.
Each one is blocking the attacking creatures chosen for it. It remains a blocking creature until
it’s removed from combat or the combat phase ends, whichever comes first. See rule 506.4.
509.1h An attacking creature with one or more creatures declared as blockers for it becomes a
blocked creature; one with no creatures declared as blockers for it becomes an unblocked
creature. This remains unchanged until the creature is removed from combat, an effect says that
it becomes blocked or unblocked, or the combat phase ends, whichever comes first. A creature
remains blocked even if all the creatures blocking it are removed from combat.
Each one is blocking the attacking creatures chosen for it. It remains a blocking creature until
it’s removed from combat or the combat phase ends, whichever comes first. See rule 506.4.
509.1h An attacking creature with one or more creatures declared as blockers for it becomes a
blocked creature; one with no creatures declared as blockers for it becomes an unblocked
creature. This remains unchanged until the creature is removed from combat, an effect says that
it becomes blocked or unblocked, or the combat phase ends, whichever comes first. A creature
remains blocked even if all the creatures blocking it are removed from combat.
EDIT: Trovata la regola precisa
Cita:
506.4b Tapping or untapping a creature that’s already been declared as an attacker or blocker
doesn’t remove it from combat and doesn’t prevent its combat damage.
doesn’t remove it from combat and doesn’t prevent its combat damage.
