To make more sense with DF and using hedgehogs, foxes, and echidnas as creatures that can cause damage, as well as some irate locals and so forth; why don't we have this done from Robotnik/Eggman's perspective? He's got tons of fortresses throughout the entire series, is a mad genius, and has countless workers doing nothing but building and maintainence for him. He only really makes an appearance when all is lost. Why not? Fortress crumbles message would be something like: "Eventually, that blue hedgehog found you and finished your Zone, and foiled your plans again. Next time Sonic, NEXT TIME!!!!"
Considering the kinds of megaprojects that would get made and everything, they would essentially become the levels of the games. I can imagine a Death Egg megaproject would be due. Just as well, don't we all make death machines of sorts? Much of them look like what the Walrus (coo-coo ka-chu) would setup in the many Zones just to kill a single elusive blue furball. A [SPEED:0] blue hedgehogman (specific megabeast caste; can be made a little more common (extra lives)) would be a nightmare. He would also maybe need some degree of [TRAPAVOID] as well (kinda wish it was more variable than a solid absolute). Do similar with the other characters. Add the suffix -man and give them their abilities, or traits close to them. Tails would be nasty to deal with. A double-tailed flying beastman that is almost as quick, has [TRAPAVOID] by default (inventor/kid genius), and can trigger levers that he crosses as well. Kuckles can also sort-of fly (glide more like). Whenever scaling (constructed) +1Z walls becomes implemented, he should be a [CLIMBINGSPEED:10] (or FAST) by default, and have a particularly nasty fist/punch damage level (with a chance of sending his targets flying/explode in gore). That should at least cover Team Sonic.
Robotnik's legions would be multi-purpose robots
EGGBOTS (not animal controlled; possibly egg-bots (as seen in Sonic & Knuckles, Sky Sanctuary Zone; usually armed with beam rifles) doing all the work building wing fortresses, plants, and bases. Migrant waves would be reinforcements. You'll need to adapt kennels or modify them into an animal conversion chamber, which converts certain animals into certain badniks (Auto war-creature option). They will serve as the defense, as they do in the original games.
I've been a fan of the classic Sonic games, and would like to see this made. Plus, I would like to see how it would be being the bad guy for once. We have easy access to Marble Zone/Lava Reef Zone, and can easily build Metropolis Zones and Wing Fortress Zones.
Some inspirational musicA little more musicBeen a die-hard fan of the Genesis age of Sonic since childhood. Not so much with the recent stuff. 2D Sonic is unbeatable (popularity-wise) compared to it's 3D future.
EDIT:
Made some adjustments.
And an additional thought (to scare Chaoseed even more): Play through all of the games (at least the first ones). They're all types of fortresses we're familiar with anyway. We have (deep breath): beach settlements, green hill establisjments, marble gardens, hill top magma pumps, oil oceans (magma/obsidian more like), scrap yards, chemical plants of sorts, azure ruins, luxurious cities made for gambling and the rich, mystic jungle villages, airbases, desert fortresses built within pyramids, ice fortresses, lava reefs, undergrottos/hidden temples, hydropolii/flooded labyrinths, and even wing fortresses/flying batteries, and hell, even floating islands, and locations flooded with colossal fungii of various colors (above and underground). Plus, with the latest features, let's make sure the minerals are easy to get (keep the mineral rarity number reasonably low in worldgen) so we can more easily replicate some of these places.
Bonus points to those that can list the zones and fotresses that match their descriptions (aside the obvious ones; still list them anyway if you can find more examples).
I don't think this mod would be out of place in DF at all. Fund it!