Normally, a unit spends 1 gas per 1 MP. The gas trick can be used to make almost any >2 MP movement cost only 2 gas!
To be more specific, the gas trick allows a unit to spend only 2 gas for any non-straight path greater than 2 tiles, or for any straight path greater than 1 tile but at 2 less maximum MP. A 1-tile diagonal approach is needed.
N xNx xxxxx xxxxxxx O = B-Copter (6 MP) xxxxxxxxx x = Gas trick possible xxxxNNNxxxx N = Gas trick not possible NNxxxNONxxxNN xxxxNNNxxxx xxxxxxxxx xxxxxxx xxxxx xNx N
How to do it:
- Select a unit.
- Draw a path to 1 diagonal tile away from the destination. You may do this with the d-pad or by dragging the stylus.
- Tap on the destination tile with the stylus, then confirm the final action. If the path didn’t redraw itself, the gas trick should happen.
You can also reach the destination tile by executing one frame-perfect diagonal movement action with the d-pad, but this isn’t recommended as it’s easier to mess up.
The gas trick is actually in every single Advance Wars game. As AW1 and AW2 don’t have stylus control, the frame-perfect d-pad diagonal movement action must be used.
As the approach to the destination must come in from 1 diagonal tile, a straight line path is only possible if the path is 2 MP less than a unit’s maximum MP. Therefore, a fighter (which has 9 MP) can use the gas trick to move 9 tiles in any non-straight path, or 7 tiles in a straight path.
Competitive multiplayer impact
The gas trick is an allowed technique in competitive PvP (player vs. player) because it takes slightly additional time to execute than just regularly moving a unit. PvP uses a turn timer, and if there are many units to control, a player may skip the gas trick if time is at a premium.
For land units, the gas trick is almost never used. There are always plenty of cities in which to supply your land units. But for air units, especially COUs and planes, the gas trick is very important. Air units have a gas upkeep of 2 for copters, and 5 for planes. In addition, air units typically dance around the map and constantly re-position themselves. Air units cannot be supplied by cities. All of this means that players will typically use the gas trick for all of their air units, or at least the key ones. When done repeatedly, air units usually won’t need to be supplied. This allows players to save the money that would’ve been used on a rig, and spend it on something else.
For example, let’s take the t-copter. Without the gas trick, the t-copter will use 8 gas per day (6 MP + 2 upkeep) as it shuttles mechs back and forth. All air units (except seaplane) have 99 gas. This means the t-copter can normally do 12 full movements before it runs out of gas, or shuttle 6 mechs from a base. But with the gas trick, the t-copter will use 4 gas per day, and be able to shuttle 12 mechs because gas consumption has been halved.
The duster is the most important unit when it comes to using the gas trick, due to its high movement, plane gas upkeep, and tendency to switch between fronts. Each day, it uses up to 13 gas: 8 MP + 5 upkeep. With the gas trick, the duster will instead use 7 gas per day and survive for at least 14 days if it uses all MP each day. As PvP games last up to 30 days, doubling the practical gas capacity of the duster is absolutely crucial.