Killers and more power variability.

The reason why a killer like Pyramid Head is good, is because he has power variability. Imagine for a minute, that Pyramid Head's only ability was his Rites of Judgment -- that would make him a pretty boring killer right? Now, the range and effects could be altered, but only having the one ability would leave him with so few options on how to play without the inclusion of perks. Freddy is also another killer that has multiple tools at his disposal.

Then we have killers like Doctor, and Plague that have variability, although to a lesser extent.

Then there's wraith. His power is just an on/off switch, and it isn't even that good because he still be seen and heard when he is too close. Yes, there are addons that change his power a little bit, but his power mostly remains the same. To new players, his ability might come off really strong, but to experienced players it's more of a minor inconvenience. Most perks can only do so much to change up the experience.

Wraith used to be one of my favorite killers, but after acquiring other killers he comes off pretty stale.

There are other killers who also suffer in the same way, but here I will give an example of how giving Wraith more power variability will make him better to both play as, and against.

1. The bell can make Wraith turn invisible, but why not objects, or even a survivor? Perhaps Wraith could be able to turn generators invisible until a survivor manages to touch it, as well making a survivor invisible to everyone including himself, but they also shimmer so other survivors need to keep an eye out for them.
2. How do survivors undo the invisibility? Around the map there could be miniature bells or something similar that can be rung to undo the invisibility that also affect wraith in some manner, like forcing him to uncloak or stunning him.
3. With the addition of more abilities, add-ons are also more varied. And because Wraith would have more opportunities to use his power, that means more chances to earn points for using them, instead of just getting points for surprise attacks and stalking.

Here's a picture to help visualize a little bit:

Of course, these are just examples, but I believe they provide enough reason for Wraith to be more than an on/off switch. If you have any ideas on how other killers can be improved on, please share them!

Some other ideas I have include:

He's "The Trapper," not just, "The Bear-Trapper." Give him other traps to use with lockers, chests, and gens!

Charging stations for Doctor to recharge, or, overcharge, to keep him from carelessly spamming it.

Hag could mark the inside of lockers that trigger when a survivor attempts to enter it.

Clown sabotaging gens to expel tonic gas on a failed skill check.