I would like to suggest Fire/Electric
dual typing, as it has an excellent mix of benefit and risk.
- Susceptible to Sandstorm
- Weak to Stealth Rock, and susceptible to Spikes and Toxic Spikes
- Weak to Water and Rock-type moves, both very common attacking types
- Earthquake, along with Earth Power and Drill Run, will annihilate this CAP unless it has extraordinary bulk, Magnet Rise, or a Balloon
- Left unguarded to most forms of priority, especially Aqua Jet
- Water/Ground-types and most Dragon-types can switch in without worries and even set-up if it lacks the appropriate Hidden Power
- Cannot switch into Dragon, Fighting, and Psychic-types too easily
- Has STABs that risk powering up Flash Fire, Lightningrod, and Motor Drive Pokemon, as well as potentially being walled if stuck with a Choice item
- Resists the VoltTurn combo
- Can switch into Bug, Electric, Fire, Flying, Grass, Ice, and Steel-type attacks, most of which are common attacking types
- Hits Bug, Flying, Grass, Ice, Steel, and Water-types super effectively
- Immune to being burnt
- Excellent lure to let Flying-types or Levitators switch in
- Capable of handling walls such as Ferrothorn, Jellicent, and Skarmory on its own, as well as stopping threats such as Scizor, Gyarados, Politoed, etc.
The charm to this typing is that not only does it have a balance of risk and reward, but that given that it both hits and resists a lot, we could easily fit this into any role, be it a sweeper, tank, wall, or support. Regarding the concept of risk, it isn't a safe typing by any means.
Say your opponent switches in Tyranitar. You are immediately presented with risk in whichever choice you make next. Do I predict Earthquake and switch into Tornadus-T, or do I risk a Stone Edge I could have potentially survived? Should I hit him with a Fighting-type move? What happens if I give Tyranitar the turn to set up Stealth Rock, do I lose or gain momentum for the battle later?
All these and more happen as you decide whether the CAP could risk its life to keep your team on the offense or to save it for whatever the situation is later.
Similarly, when CAP4 is on the field, your opponent is stuck in a risky situation as well. What set is it running? Should I switch, or would he be predicting that? Could my team handle it if I lose my Ground-type on a misprediction?
True mind games indeed for everybody.