matter - Are there different kinds of antimatter reactions?

Obviously, when matter and antimatter collide, they annihilate. But how exactly and are all reactions the same? For example, what happens when a molecule of hydrogen meets a single pion? Does the single anti-down quark in the pion react with the single down quark in the proton? If so, what happens to the single up quark remaining in the pion? It can't exist alone? What about an anti-proton? Would it annihilate just the proton, or the electron too?

Also, is the explosion caused by the proton/anti-proton the same as that caused by the electron/positron annihilation? And is the explosion caused by helium/anti-helium annihilation simply the sum of its smaller parts annihilating? Or, does it equal something more? Thank you.