Can instants be cast after blockers declared?

You can cast instants and spells with flash before blockers are declared. You can cast instant spells any time you have priority, including after attackers are declared and before blockers are declared (C.R. 116.1a, 508.2, 116.3d). See also this thread.

Does blocking in MTG tap the creature?

A creature must be untapped in order for it to block. Unlike attacking, the act of blocking does not cause the blocking creatures to tap, and creatures with summoning sickness can block.

Can instants be blocked?

To answer the question in your title, yes, each player receives priority and can cast instants after blockers are declared. However, to answer the (unwritten) question in the body of your text, the attacking creature will still be considered blocked, even if the defender is killed or otherwise removed from combat.

Can you activate a tap ability when blocking?

Yes. A blocking creature may be tapped to pay a cost or as the result of an effect. This has no effect on its status as a blocker. It will still deal and receive damage as normal.

Can instants be played whenever?

Instants are the only card type in Magic, something unique to it compared to other card games, to have no timing restrictions. They can be played at any time one has priority, including during other player’s turns and while another spell or ability is waiting to resolve.

When to cast instant to prevent a creature from blocking?

The last time you can cast an instant to prevent a creature from blocking is in the Assign Attackers step, after attackers have been declared. If you have moved to the Declare Blockers step, it’s too late, since the very first thing that happens is the defender declares blockers. Nobody has priority until after that happens.

What happens when you block an opponent’s creature?

A blocked creature will deal no damage to the defending player unless it has trample (or some other card-specific ability). It sounds like you want to kill an opponent’s creature before blockers are declared. Your last chance to do this is when you receive priority after attackers are declared.

Can I cast instants in response to my opponent declaring?

When my opponent declares blockers, I want to be able to kill a blocking creature (with something like Hero’s Downfall) while still doing combat damage to my opponent. Is this possible? To answer the question in your title, yes, each player receives priority and can cast instants after blockers are declared.

When does an enchanted creature can’t be blocked?

Enchanted creature gets +1/+0 and can’t be blocked. Enchanted creature can’t be blocked. Whenever enchanted creature attacks, scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)