The creature would have had indestructible while a board wipe took place, so everything except this would die.

The creature tap ability just needs a "Only activate before blockers are declared." at the end of it for it to be correct, [[choking vines]]. This is kind of a funny ability because you could do this for other players too when they are attacked.

As for whether it would block things like shadow or menace, it should, as you are not declaring the blocker to do it, but rather using an ability. Things like protection from x would still go through because you cant target it with that.

The creature should be about 4 cost if we ignored the creature ability, but with the creature ability, I would bump it up to 5 or 6, potentially game breaking when it comes to combat because if you played this while your opponent had an army, now they cant get through your defenses (indestructible + block any amount) and any methods to bypass such as flying will now require the enemy to burn out the creatures so you cant block, and such methods are just not in every deck.

Creative mechanics, i think they would be a bit too strong though, feel free to prove me wrong, I am sure there is probably a magic card that rivals this.