What can your character do? What are they good at, and what are they like in battle? This is important to know; especially in wartime!
Weapons & Combat Style
When it comes to war, everyone needs to carry some kind of weapon with them to defend themselves. A good rule of thumb is to pick at least two weapons; a long-range weapon (so they can attack an enemy that's farther away) and a close-range weapon (so they can attack an enemy that jumps in front of them). You can most certainly have more, but not too many; I'd recommend having no more than five different weapons, though there may be multiples of them (for example, one weapon is missiles, but there are three of them). When allowing for multiples of weapons, try not to exceed ten total pieces of weaponry as this begins to get a little extreme. You might be able to skirt around this rule a little with a very big character that turns into something like a large military bomber, but don't go crazy.
When choosing your weapons, be mindful of what kind of character you have. If you've chosen a military vehicle as an alternate mode, research what kind of weapons are attached to them. An aircraft might have several missiles; a ground vehicle might have a machine gun turret. Also keep in mind what your character will be able to carry; where are these weapons going to go? Don't just throw a bunch of weapons on them and say that it works. Let's look at some examples;
Character X: A large, military aircraft. His maximum possible weaponry could include;
-Three or four missiles in a bomb bay
-Laser-guided munition (rapid-fire, long-range; stored in secondary weapon bay)
-Two swords OR rifle OR machine gun/bazooka/rocket launcher (stored on his back)
-Two handguns at his hips (one on each side)
Twin punching daggers OR twin swords OR twin plasma guns (stored in forearms)
-Daggers OR whip OR lasso OR something else (stored in leg panels)Character Y: A petite sportscar. Her maximum possible weaponry could include;
-Two handguns at her hips (one on each side)
-Two swords OR rifle OR machine gun/bazooka/rocket launcher (stored on her back)
-Twin punching daggers OR twin swords OR twin plasma guns (stored in forearms)
-Daggers OR whip OR lasso OR something else (stored in leg panels)The examples above are going a bit over the top in terms of weaponry and do not have to be multiples, but you can get an idea of where some of these weapons might be and how much a single Cybertronian could carry at maximum. I've chosen not to include "natural weapons" such as fangs and claws (if they have them), because I don't think those count to the "number of weapons" rules.
Something that goes right along with their weapons is their fighting style. Not everyone fights the same way! If you gave your character a pair of swords to stick on their back (katanas, perhaps), maybe they fight in similar fashion to one of the older Chinese or Japanese styles. A character with a long, slim sword might choose an elegant fencing style, while one with a larger, bulkier sword might go with the rough slash-and-stab style. If they are equipped with a rifle, perhaps they fight like a sniper; striking down their enemies from afar with deadly accuracy. A machine gun might indicate a rougher, more reckless combat style. Think about how they use their weapons, rather than just slapping some on them!

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How To: Making A Transformers OC
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