BushidoBushido is a triggered ability. “Bushido N” means “Whenever this creature blocks or becomes blocked, it gets +N/+N until end of turn.” (See rule 509, “Declare Blockers Step.”)
If a creature has multiple instances of bushido, each triggers separately. (CR 702.45) 1 (Whenever this creature blocks or becomes blocked, it gets +1/+1 until end of turn.)
Whenever a creature an opponent controls
diesIs put into a graveyard from the battlefield. (CR 700.4), you may
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) target instant card from your graveyard. If that spell would be put into a graveyard,
exileTo exile an object, move it to the exile zone from wherever it is. See rule 406, “Exile.” (CR 701.13) it instead.