One thing that's important to keep in mind is that creatures can have negative power. If you hit a Bouncing Beebles with Shrink, they're going to have -3 power for the turn, not just zero. Normally this is of no consequence, since a creature with negative power will still assign zero damage, but for our purposes today it's key that the game still tracks negative values of power. The trick is to find some use for a creature's power rather than just assigning combat damage.
Here's an easy example to start us off: consider Auriok Bladewarden. He can tap to pump a creature up - the bigger he is, the bigger a boost he gives. But what happens if you hit him with Chant of the Skifsang? Now he's got -12 power. He can still add his power to another creature, but what happens if you add negative twelve to a number? Why, it goes down by twelve! He can tap to give any creature a staggering -12/-12! You've achieved a mini-Visara in blue and white that can start firing off as early as turn three. Why use the Chant as a weak form of removal when you can transform it into a fearsome death cannon? Rabble-Rouser can serve in a less lethal capacity in red, letting you fog your opponent's whole board every attack. The result is kind of a colorshifted Dawnstrider (that doesn't even require a discard)... how very un-red!
Of course, adding negative values is pretty crafty, but there's nothing quite like a double negative to result in an unexpected boost. Giving a creature -13 power is a pretty hefty drop, but why settle for the double digits? Our favourite accidental monkeys, Hyalopterous Lemure and Viscid Lemures, can lower their power at will as often as you want. So if you lower a Lemure to -500 power, you can then sacrifice it to Ichor Explosion in order to... give every creature +500/+500! That's a pretty wild board state. If the seven mana for the Explosion is a little too hefty, Call for Blood can be had more cheaply and will probably be a win if you throw the bonus at your Invisible Stalker.
While the usually-fatal practice of reducing a creature's toughness is costed around par with most other removal, reducing power is generally a lesser solution and thus costed much more cheaply. So why not take advantage of this fact? There's no greater thrill than bamboozling your opponent with a rules interaction that makes sense but would never occur to the average player. Just don't be too surprised when suddenly everyone wants to trade you for your copies of Disorient and Constricting Tendrils.
