Difference between throwing and droping
Just chiming in on the people who don't believe that you can kill someone with a penny.
The terminal velocity of a penny is only about 67mph. However Terminal velocity is using the only relevant force being gravity acting on the object. When you throw something you apply additional force which allows you to exceed the terminal velocity of the object. For comparison the terminal velocity of a baseball is around 89 mph where as there are pitchers whom can get the ball moving as fast as 110 mph.
Presumably this is the point at which Max realizes that he needs to teach Amber strategy and tactics as well as technique. The person who can improvise well will beat the person who can strategize well 90% of the time, because no strategy can take into account all possible reactions. Do something clever and unexpected, and you regain the element of surprise.
For examples, see Timothy Zahn's Thrawn Trilogy, the entirety of Death Note (while both Light and L had long-term strategies, they were both forced to constantly adapt and improvise), and EVERY WAR EVER IN THE HISTORY OF MANKIND (WWII has some particularly good examples: see Gen. Patton and the Battle of the Bulge.).
I actually think it's a really good point of characterization that Amber and Gail think in such different ways. While Gail was forced by circumstance to turn her obvious intelligence and cunning to figuring how to get herself out of bad situations and both be and appear tough enough to not be put into them in the first place, Amber probably never had to strategize any further than planning the most efficient route through the mall.
They say that the person who wins the chess match is the one who thinks the most moves ahead. (While this may seem to disagree with my first statement, chess pieces are a lot more predictable than people. Hollywood history shows us that any character who reduces everything to a chess analogy will lose.) Again, it's clear in this case that Gail wins. Amber's thought process seems to have been, "I'll take Gail by surprise and defeat her with my new coin trick," whereas Gail, although confident that she could defeat Amber, has already called for backup.
Thus far, Gail wins at both strategy and tactics -- *and* she has that constantly changing superpower which, while problematic, is also impossible for the enemy to plan for. Sorry, Amber, but Gail wins for the foreseeable future.
Um, I hope you like long comments. I analyze everything this way. (It drives my family absolutely insane.) Big fan of the comic and I can't wait to see how things turn out!
Well, sorry for the pun barrage, it should make you happy that I am having difficulties with this one... ooooh, got one. Looks like Amber better duck and 'cover'. Bit of a stretch, but it was the only one worth mentioning.