Today, I'm going to spoil the six bosses from the original Mega Man. Additionally, the set includes each boss's related special weapon, so I'm going to include those as well.
Cut Man's scissor attack could hit you twice if you were poorly positioned, so I decided to go with double strike for his primary effect. And if you look at the history of Magic, 3 power double strikers are pretty rare. As far as the second part, it was a stretch, but I decided that the fact that there are those two blocks in his lair was enough to do something with artifacts.
While not all weapons fall into this category, with the Rolling Cutter I was able to give the equipped creature a similar effect to the boss from which you get the item in Mega Man. I wanted to make it a little more nuanced, hence the second part. By the way, as far as mana costs for the equipment: in general, I tried to have the casting cost be relative to the difficulty of the boss, and the Equip cost relative to the energy cost of actually using the weapon. It didn't always work out this way, but that was where I started when building the weapon cards.
So, for Fire Man, I actually used his flavor text (taken from the Mega Man comics) to develop the card's main effect. Fire Man was a bastard to fight against, always seemed like he was blasting me insanely quickly, so I gave him haste as well. Fire Storm again draws from the boss's card, but also from the effect of the weapon itself, which creates a little bubble of burn around you for a moment. The mana costs were based again on the difficulty and cost of the weapon, but also on the fact that giving the ability to deal 1 damage to all opposing creatures any time you attack was an effect I didn't want available on turn 2.
Ice Man is another guy who I crafted around his flavor text. He's not wildly powerful; a 2/2 for 2 is available in most colors, and in a multicolored card, 2/2 for 2 is actually a little behind on strength. But somewhere in the set, I wanted to make a card that could wreck in a blink deck, and I think Ice Man takes pretty good advantage of that with his two effects. Ice Slasher is the first of these weapons to not draw from the boss's card, but it plays better to what the weapon's effect is in the game.
Once again, the flavor text comes into play for the creation of the boss card. The idea here is that Bomb Man, while not particularly strong, brings bombs into the equation. When he does, other people (or "Idiots!" as he calls them) who don't know how to handle bombs end up dead. Hyper Bomb was my attempt at creating a "fuse" mechanism in Magic. I had to retool it a couple times to get it right, and to make sure it couldn't be used by a creature enchanted with Claustrophobia, Encrust, etc.
Elec Man is a high octane enemy, so I knew he had to have high power and trample. As you may be coming to expect by now, I also used the flavor text to further develop the card. Thunder Beam, as you can see, sends beams in three directions. That's what I used to determine the effect of the card. I've already had dreams about equipping a double strike creature with Thunder Beam and clearing an opponent's board.