My OCD doesn't like 4 keystones in only 2 pages. So here's 3 Keystone suggestions

Precision and Domination have 4 keystones while the others have only 3. I don't think this is fair!

Also I have free time and like theory crafting this sort of thing. So here are 3 keystone idea's I came up with!

1:

Mythic Armory - Sorcery Tree Can hold up to 3 charges After damaging an enemy champion with an ability your next basic attack within 6 seconds deals 10-50 (+20% Bonus AD)(+15% AP) and consumes a charge After damaging an enemy champion with a basic attack your next ability within 6 seconds deals 15-60 (+25% Bonus AD)(+20% AP) and consumes a charge Gain 1 charge every 10 seconds (14 seconds for ranged champions)

The idea is that an AP melee champ like Sylas or Akali can take thus rune and quickly alternate between ability damage and auto's to expend all 3 charges very quickly. Some ranged champions will likely like this as well such as Kogma or Ezreal, since it means they can get another AP ratio on their auto attacks if they decide to build AP.

Due to how the Keystone gets multiple procs back to back, the AD and AP ratios are a much bigger part of the damage compared to other keystones such as electrocute. Because of this I'm not sure the ratios I gave it are what they should be, but it is intended to scale off items really well.

(Omnistone grants 3 charges of this keystone and won't regenerate them. Keystone is used up when the charges are consumed)

2:

Ghostly Crest - Inspiration Tree After last hitting a minion it will spawn an allied ghost minion in it's place. Ghost minions will follow you around and will attack the same target as you (damage dealt this way counts as damage dealt by you) You may have up to 2-10 Ghost minions alive at a time. (gaining 1 every 2 levels) Ghost minions lose 2% of their max HP every second. Ghost minions take 50% more damage from all sources. Killing a Ghost minion grants you 1 gold (for the same reason as zombie wards)

Primarily for champions with good waveclear that want to perma-push. Having Ghost minions that attack the same target as you will improve your pokes, since minion damage is fairly meaningful in the early game. Meanwhile in the late game this Keystone lets you turn enemy minion waves into friendly minion waves, which massively accelerates pushing. Top lane split pushers like Nasus can use this to improve their push potential by reducing the need to wait for a friendly minion wave, while those who like to group would use this to improve their ability to siege.

(Omnistone cannot grant this rune)

3:

Embalming touch - Resolve Tree Basic attacks, abilities, item effects and summoner spells generate stacks on enemy champions hit, up to one per attack or cast. Applying 3 stacks to a target within a 5 second period causes them to lose 20% tenacity and reduces their damage dealt by 20% for 3 seconds. If they are immobilized during this time they take 15-75 (based on level)(+20% Bonus AD)(+15% AP) physical damage.

25 second cooldown per effected champion

Designed to be more for reducing damage on others rather than just for tanking the damage yourself, a bit like a more aggressive Guardian. Ideal for mage supports that want access to the Resolve tree while still maintaining aggression. Also likely would be good for some toplaners who use CC in the middle of their combos like Kennen.

Not designed for traditional tanks as they would prefer to just go aftershock or grasp of the undying. Can also be used by marksmen wanting to set up their support by first removing their tenacity and then having the support go in and lock them down.