The Power of Multitasking: Combination Attacks in BBP
If you've ever seen the Pokemon anime, I'm sure you're familiar with the way the show's Trainers like to combine moves flavorfully in battle. They don't just use Aqua Jet, they shoot an Ice Beam at it to turn it into a Slip-n-Slide. Or, they'll have a Pokemon use Flamethrower on a Whirlwind to make a fire tornado or something. In Battle-By-Post gimmicks like these are called Combinations, and are legal techniques. As a matter of fact, they're such an integral part of the game that you probably won't get very far in your career as a Trainer before somebody uses one on you.
On a basic level, Combinations synthesize the traits of two moves that a Pokemon knows into one hybrid move. For example, a Combination of [Aqua Jet + Scald] would cause the user to jet forward on a stream of boiling-hot water with Priority and a chance to burn, whereas [Stun Spore + Poison Powder] would release potent spores that Paralyze and Poison simultaneously. Almost anything your imagination can come up with is valid, so long as the Combination is logically feasible -- [Earthquake + Thunder] won't work because the moves can't be combined in a logical manner*. Or, if you're not the creative type, just combine a move with itself ([Razor Leaf + Razor Leaf]) for a multiplicative power boost. With a wide enough movepool and a good head, it's possible to come up with Combinations for solving all sorts of problems as they arise.
As you might imagine, there are many strategic applications for Combinations. Is your 1HP Pokemon about to get KO'd by a faster Pokemon? A combination of a Priority Attack and a high-damage move ([Quick Attack + Giga Impact]) will make for a rude parting gift. Want to use a high-damage move like Thunder but you can't afford to miss? Combine it with the sure-hit move Shock Wave for guaranteed success! Oh, and here's a fun one -- tired of your opponents spin-blocking you with their Ghost-Types? If so, combine Rapid Spin with a move of a different type to override its Normal typing! So long, Stealth Rocks!
Combinations are ridiculously flexible, though they are not without drawbacks. For starters, they put great strain upon the Pokémon performing them. You see, Combinations are so physically taxing that the user cannot act on the following turn (you'll hear players refer to this as a Cooldown action). If your opponent sees it coming, they can simply Protect against your attack and punish you during the following Cooldown action -- perhaps with a Combination of their own! That's why, as a general rule of thumb, it's best to only use Combinations after your opponent has already ordered. Otherwise it's usually safer to just order single attacks instead. Furthermore, Combinations are typically associated with high Energy costs. Use too much Energy and your Pokemon will faint, so be careful!
So there you have it: the basic rundown on Combinations. Use them carefully, use them strategically, but above all, use them creatively! I'm serious! If you're not sure whether a Combination you're planning on using is feasible or not, you can always just ask your ref. I'm still waiting for somebody to convince me that [Earthquake + Thunder] is feasible. I don't know what it'd look like, but I'm sure it would be totally sick. DM me.
*Out of the ~728 known moves, the only ones that CANNOT EVER be used in Combinations are: Assist, Bide, Copycat, Endeavor, Endure, Me First, Metronome, Mirror Move, Nature Power, Sleep Talk, Substitute, Transform, and Z-Moves. These moves are generally either too random or too unique to be workable. This information can be found in the Data Audit spreadsheet, which is the repository for all BBP data; moves that cannot be used in Combinations are listed there with a "Combo Type" of "None".