That is F#%&ing awesome.
Very different to the world that I was building but awesome nonetheless.
I like the suggestion of using a different ruleset for the characters outside the mechs. If the size difference wasn't too great between to two, (say, if the mech's where large, or , at the most, huge), you could actually use 3rd-ed based rules for the characters outside of the mechs. d20 Modern would probably be the best fit.
The rational here is that they would still be able to interact, and possibly even fight each other, but there would be a distinct and noticeable difference in power between the two.
Characters on the ground would have less hit points, deal less damage, and would not have healing surges or regular powers. With the right equipment and tactics, they could probably deal with a mech, but not easily.
It could also be interesting to increase mech-size with tier.
Heroic Mechs would be Large
Paragon Mechs would be Huge
Epic Mechs would be Gargantuan
This scaling would only really come into play in the human-scale part of the game.
It could easily be reversed though:
Large Mech scale: 4 medium creatures can fit in one square.
Huge Mech scale: 9 medium creatures can fit in one square
Gargantuan Mech scale: 16 medium creatures can fit in one square.
At these larger scales, mech powers that target a creature can target a square instead.
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A few modifications would sill be have to made to allow the two combat systems to dovetail more smoothly. (whether you'll use grab or gapple, five foot steps or slides, etc)
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Skills:
Skills would have to be streamlined a little (Trained/untrained rather than ranks, Using perception rather than spot, Listen & search, etc.)
The Mechs and the pilots each have different sets of skills.
Skill Synergy: If a mech is piloted by someone with overlapping skills, then the mech gets +2 to each skill that the pilot is also trained in.
(This means that some people are well-suited to their mechs)
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Hit Points:
Mechs and pilots have separate hit point totals.
Pilots gain half their Hit dice type per level.
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Levels:
A simple system to allow d20 Modern characters to get to 30th level would be needed.
This could easily be an extension of the existing tables, and the focus in Modern on multicalssing would work well with this.
Both the mechs and the pilots would need to gain experience and level up at the same rates.
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A note on Bio-Mechs:
Rather than seeing these as transformers, I’d see them as much more similar to the Evas from Neon Genesis: They are biological, they are alive, and are sometimes barely restrained by their technological shackles
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Should this stuff be forked into a new thread?