Wolverine’s Frenzy: When you damage an opponent and the damage die is an even number you deal 1d6 extra damage and gain +3 Vigour for the rest of the encounter.
Pack Tactics: Add 1d8 to your damage when you have advantage on the Hit Roll OR against a target threatened by one of your allies.
Cave Bear’s Rage: When an enemy damages you, you deal 1d10 extra damage for 1 round.
These perks all change the way you want to play and what sorts of decisions you will make. I like that generally and I think the perks do their thing just fine. However, there aren't any decisions to make as characters level up and the perks are kind of limited in how complicated they can be. I want to be sure that first time players aren't overwhelmed by perk mechanics so simplicity is crucial. On the other hand if I had room for more complex mechanics my creative space would be a lot bigger.
Thinking about these things I came up with an idea for expanding perks. My thought is that each time a character reaches a level divisible by 8 they can either take a new perk or upgrade an old one. The upgrades should be roughly equal in power to the basic perks but because they are locked away until higher levels I am much more willing to do wild and wacky stuff. I can up with a bunch of examples to see how it would work. Here is one of them:
Rank 1: You no longer take disadvantage when making a Hit Roll against a target with Cover or Concealment. You gain a +1 bonus to Hit Rolls.
Rank 2: Increase bonus to Hit Rolls to +3.
Rank 3: You deal 1d10 extra damage when you have Cover or Concealment from the target.
Rank 4: When you attack you can measure line of sight as though you were standing in any space that is adjacent to you.
That fourth rank is crazy! Shoot around walls! I wouldn't want to put that in as an ability for starting characters as it requires you to understand line of sight and is really only good when you can abuse that but for someone who is near max level it isn't out of line at all.
There are some issues to doing this. It will increase character power ramp up so I will have to account for that in designing opponents and figuring out encounter strength mechanisms. However, I think it will give people some interesting things to look forward to when they do get more powerful and having these additional choices will make for more variety in character design. Right now the upgrades are all designed to be equal in power but I could potentially make them way stronger and more exciting at the top levels to give players really amazing abilities. Taking a different perk instead of an upgrade would never be the right choice though, so that set of options would be cut off. For now I am mostly set of building these expanded perks as being equal in power to each of the basic choices and going from there.