I was talking with one of the competitive Pokémon players here on Paint in a chatroom the other day, and talking with them helped me to realize that the primary difference between me and most of the other skilled Pokémon players here is not my lack of competitive battling experience (depending upon one's definition of "competitive battling", of course), but rather is due to the fact that almost all of my online battles were Triple Battles, and (AFAIK) all of the competitive Pokémon players here only do Singles and/or Doubles.

While it's true that there are a number of similarities between Doubles and Triples, Triple Battles are not merely Doubles with 1 extra Pokémon on each side, and there are a number of significant differences between the 2 formats, which is what I will be touching on in this blog series.

1. Positioning

The effect each Pokémon's position has on which Pokémon it can hit (and which Pokémon can hit it) is the biggest difference between Double Battles and Triple Battles.

A Pokémon can only hit other Pokémon in positions adjacent to their own (unless a long distance move is used), whether they are using a single target move, or a move that hits multiple targets.

This means the Pokémon in the central position is capable of hitting (and being hit by) all 3 opponents, as well as both of it's allies.

The 2 Pokémon on the ends, on the other hand, are safe from the opponent's Pokémon on the opposite end of the battlefield (again, assuming they don't have any long distance moves), but can't hit the Pokémon on the opposite end themselves, either.
(They also can't reach their ally on the opposite end of the battlefield, either.)

Additionally, the 2 side Pokémon can shift positions with whatever Pokémon happens to be in the center ATM, and when this occurs is determined based upon the side Pokémon's Speed Stat, rather than the Speed Stat of the center Pokémon.
(This is relevant for a number of different reasons, which I will discuss in future blogs.)

2. Long Distance Moves

All single target Flying-type moves, and all of the "Pulse" moves (Water Pulse, Dragon Pulse, Dark Pulse, Aura Sphere, and Heal Pulse) are capable of hitting any Pokémon on the battlefield, regardless of the target's or user's positions.

As a result, there is a stong incentive to have Pokémon with such moves in the side positions, and Pokémon that are good at using such moves (such as Rayquaza, Mega Blastoise, Lucario, and Togekiss) are WAY more useful in Triples than they are in Doubles, as a result.

3. The Center

The Pokémon in the center doesn't really need to worry about long distance moves, and should instead focus on moves that hit multiple targets, as well as defensive moves.

Multi target moves can hit all 3 of your opponent's Pokémon if used by the Pokémon in the center, whereas the side Pokémon can only hit their 2 closest opponents.

Like in Doubles, such moves (assuming they are attack moves, and not multi target status moves, anyway) inflict 75% of the damage they'd inflict in a Single Battle.

As an example, if you use Earthquake from the center position, it'll be the equivalent of hitting all 3 of your opponent's Pokémon (and both of your other Pokémon, as well) with a 75 Power Ground-type move simultaneously, which is VERY powerful!

Because of this, multi target attacks and status moves (like Dark Void) are EXTREMELY powerful in Triples, particularly if used from the center position.
(Initimidate works well from the center position, too.)

It is also a good idea to have Pokémon in the side positions that are immune to the center Pokémon's multi target moves, if necessary.
(Flying or levitating Pokémon to avoid Earthquakes, for example.)

4. 2 Turn Moves

I've gotten a lot of criticism for recommending the move "Fly" for Landorus in one of my Moveset blogs before, and their argument was that the move was a "dead giveaway", and was therefore completely useless.

Now, regardless of whether or not this is true in Single Battles, or even in Doubles, it is most certainly NOT the case in Triple Battles, and I'll explain why.

First of all, such moves (Dig, Dive, Phantom Force, etc.) can be used against any of the opponent's 3 Pokémon, if used by the center Pokémon.
(And Fly can hit any target regardless of the user's position.)

Now, assuming your Pokémon is faster than all 3 of your opponents, you'll be able to avoid whatever attacks they send it's way during the 1st turn (it's a common tactic to gang up your opponent's center Pokémon, because they are the most vulnerable, BTW), and in the 2nd turn, your opponent will be forced to guess which of their 3 Pokémon yours is targeting, potentially putting them in a difficult position.

Even if there is an obvious target, you don't necessarily have to go for it, and as a result, you can take advantage of these moves in a variety of ways in Triple Battles.