[YuuchyShi]

I'm thinking something like Normal/Ice. Normal doesn't add much to ice's resists, only adding an immunity to ghost. It does give boost Ice's weakness from 2x to 4x, so there's something. Ice doesn't help much with Normal's fighting weakness, and normal doesn't do much to mitigate the ice resistance steel has. Ice keeps every weakness it has. The rest I'll use those five important things BMB mentioned.

Passive damage weakness: -1/4 every time it switches in with SR on the field, takes damage from both kinds of spikes, leech seed, and sandstorm. Sun boosts fire, rain boosts water, and they both boast an resistance to ice. It can be burned, toxic'd, slept, paralyzed, and frozen, though the last one isn't going to happen much. It is neutral to U-turn, Volt Switch, and Pursuit.

Good Overall STAB Combo: Well... Normal/Ice can... uh... do great damage to... ah... Nothing?

STAB that cannot realistically be spammed endlessly for maximum impact: Had to copy and paste that one. Well anyway... The last bullet addresses this, but I'll state some things that didn't apply to that one. You can spam the normal side of the spectrum if you've already gotten rid of Ghosts, Steels, and Rocks, although (if it's not a choice set) you could throw on some coverage and you're good in terms of type coverage. But honestly, who spams a normal move?

Lots of weaknesses and resistances: On the weaknesses side, ice doesn't get anything new. It does get a buffer on it's ability to switch in, though. Just switch it in on a Ghost move.

STAB on notable risky moves: Stab on something with a bad side effect? Giga Impact. Hyper Beam.

Well, that doesn't really fit a bit of the criteria, but I spent around 5 minutes typing that, so I'm not going to erase it. If anyone can see something good about that typing, well, perhaps you could say it. Because that one was actually ok, I'm going to suggest Normal/Dark. That typing- You know, I'm just going to skip to the 5 important things.

Passive damage weakness: 12% on SR (I think), both spikes, leech seed, all weather (that deals damage), and U-turn. Hit normally by Volt Switch, resistance to pursuit.

Good overall STAB combo: Normal/Dark can hit everything for neutral except Steel, which is commonly seen, but easily ignored with a coverage move. Or the amazing reward that will come in another category (trying not to poll-jump).

STAB that cannot realistically be spammed endlessly for maximum impact: The typing is basically: See a steel? Switch out!

Lots of weaknesses and resistances: Both the typings I've said so far have a unbroad range of weaknesses and resistances. Hit hard by bug and fighting, not hit at all by Psychic and Ghost, resistance to Dark. This gives this guy a huge amount of chances to switch in, but not a lot of chances to stay in. A steel or a fast fighting type (Mienshao or Mach puncher/vacuum waver) would kill this guy faster than a fire fang would kill a ferrothorn. Unfortunately, this typing doesn't do much in this section.

STAB on notable risky moves: Sucker Punch, Giga Impact, Hyper Beam, Pay Day, Explosion, Selfdestruct, Payback, Covet.