Can someone cite some rule(s) for this? I did before asking the question consider rule 509.1 and it is what made me confused about it.
As in, the wording of Shinen of life's roar seems to be one requirement that is satisfied if all creatures able to block it does so (because that is what the card says). In that case, it would be valid to block just the bear with the bear that got hunt down (in my example), because both my bears blocking shinen would satisfy 1 requirement (shinens) and blocking the bear with the hunt down bear (no matter what the other bear was doing) would satisfy 1 requirement (the one made by hunt down).
Seemingly, from what everybody are saying (which was also my first thought before I got unsure) Shinen makes multiple requirements even though the text says something else. Which rule does that?
C.R. 508.1d and C.R. 509.1c are the rules that govern attacking requirements and blocking requirements, respectively. However, it is unclear according to those rules—
whether an effect of the form "All creatures able to block [a given creature] do so" imposes one "requirement" (within the meaning of C.R. 509.1c) on each creature "able to block" the given creature, or one "requirement" generally, or
whether the effect of War's Toll's second ability imposes one "requirement" (within the meaning of C.R. 508.1d) on each attacking creature, or one "requirement" generally.
The answer has a bearing on whether certain attacking or blocking declarations are legal in certain circumstances. See also this thread.
An effect of the form "All creatures able to block [a given creature] do so" applies only to creatures "able to block" the given creature (review C.R. 509.1c). For example, for the purposes of such an effect—
a creature with the ability "[This creature] can't block", such as Carrion Feeder, is not "able to block" any creatures,
a creature is not "able to block" a creature with the ability "[This creature] can't be blocked", such as Unimpeded Trespasser, and
a creature with neither flying nor reach is not "able to block" a creature with flying (C.R. 702.9b).
C.R. 508.1d and C.R. 509.1c are the rules that govern attacking requirements and blocking requirements, respectively. However, it is unclear according to those rules—