I have to make sure my post is talking about the latest Metal Slug Defense at the time of writing - V1.15
From time to time, the Metal Slug Defense rolls out new units. It has been a hot topic about 'which unit is the strongest' in this game. For sure, not only the strength or attack power, the 'Cost effectiveness' is critical too.
Undoubtedly, the land unit like Leona, Morden Robot, Jupiter King, etc are the most voted units. They have been proved efficient and powerful during a 1 vs 1.
However, in this post, particularly, i would like to talk about the Air Units (eg: R.R-Shobu, Samurai Plane, Slug Copter, Flying Tara, Hover Units). Not all of them are free, but it is worth mentioning that some of them are special during the battles.
The one capturing my eyes the most, is the R.R-Shobu, the red air fighter. Why?
First, Air units are generally 'overlooked' by the AI. Often, if you only summon air units, the enemies are unaware of your troops, and thus, they don't attack you! One of the great examples is the 'Big Shiee' from China. Remember the last post on the China? The fact that the Flying Tara is able to strike the Big Shiee so effectively is mainly due to the fact that the latter doesn't detect it in the radar at all!
Second, the R.R-Shobu is one of the few air units having the special skill. By default, the R.R-Shobu launches a few missiles while regressing (to avoid enemies' attack). Then, he will launch a final bombing to the enemies after finishing the missiles.
Now, the thing is, the special skill of the R.R-Shobu is able to 'Reload' the ammunition! Meaning, if you activate the skill of R.R-Shobu at the correct timing (just after he has finished the bombing), he is able to re-launch the missiles and the bombing.
With this skill, the power of R.R-Shobu doubles! Together with the first advantage, it is to say that, the enemies are being bombarded with attacks without a counter-strike!
I have made several experiments. Air Units alone are sufficient to handle most of the stages, including those from the latest and more difficult maps!
The only prerequisite is the AP costs. Once you have upgraded the necessary HOME units (and rescue POWs accordingly), you will definitely be able to unleash the awesomeness of the air units in the Metal Slug Defense!