By "wanton maliciousness", I meant malicious behavior perpetrated for no reason other than satisfying some perverted/deranged/"evil" urge, impulse or desire on the part of the perpetrator unconnected to other "morally neutral" behaviors, like eating or otherwise "surviving"...
Some of your examples, I guess I'd have to agree with... though without necessarily agreeing with them, I also have to acknowledge that mainstream animal behaviorists usually "explain away" many of the behaviors you point to (like the mice "bullying" each other) as being based on instincts/behaviors that wouldn't normally be conflated with "wanton maliciousness..."
But as for some of the others - "revenge" for being shot is "cruel"? By whose definition? Even human homicides are often (though not necessarily) deemed rather less than "murder," much less aggravated murder, under similar conditions. And when it is considered "murder", that's based on the idea that the person has more appropriate alternatives. What's the tiger's alternative? Seeking legal redress? Or simply "turning the other cheek"? (We know how popular that is even among the most assertedly devout Chiristians and for that matter, until quite recently in historical terms, the Church hierarchy as well...) And it's not as if ridding itself of the hunter is purely "vengeful" either, rather than removing a potential future threat as well...
As for the mouse eating the other mouse's leg, again, "eating" "food" strikes me as definitely not "cruel" as the word is usually used, even while the other mouse was still alive, considering that animals often (have to?) eat other animals while they're alive... Are snakes being "cruel" to the rodents they consume whole (and which I've always assumed to my personal horror must survive, if only for some very brief period of time, inside the snake's "mouth"?) For that matter, are humans being "cruel" when they eat live shrimp (which I personally find abhorrent, but is considered a delicacy by some/many Chinese)?