Merlin's Ward [Item Concept]
Recurve Bow
+ Seeker's Armguard
+ 800g = 2900g total
35 Ability Power 25% Attack Speed 45 Armor
Passive: Basic attacks deal 5(+15% AP) magic damage on hit.
Unique: Basic attacks grant 8% attack speed, 2.5% AP, and 2% pre-mitigated damage reduction for 5 seconds, stacking up to 6 times, granting a maximum of 48% attack speed, 15% AP, and 12% pre-mitigated damage reduction. At 6 stacks, gain MERLIN'S MIGHT. While at half stacks, melee champions' next basic attack will fully stack Merlin's Might.
Unique: MERLIN'S MIGHT: Half of the damage reduced by this item is reflected back at the attacker.
As you can tell, this item is very inspired by Guinsoo's Rageblade, but it is definitely more of a tank item. I wanted this to be for champions who scale with Ability Power, and excel in prolonged combat.
Gold efficiency 35 Ability Power [761.25g] 25% Attack Speed [625g] 45 Armor [900g] Total 2286.25g
Like with Guinsoo's Rageblade, this item is 70-80% gold efficient, but with full stacks it is closer to 200% gold efficient, or more when combined with other items.
I was initially considering this item with a Ruby Crystal, but I decided to intentionally not give flat health for this reason. I felt that Armor and Damage Reduction would be too strong when combined with flat health in the same item The player will need to buy a different item to give them Health, Magic Resistance, and/or additional Ability Power in order to increase the effectiveness of this item.
This would definitely be a good item for AP tanks
who also work well with on-hit damage, and AP fighters/skirmishers that need more resistances to survive extended fights

I'm also going to throw this in here because I get these comments every time I pitch an item idea on here. No, this item is not necessary. None of these champions "NEED" this item in order to be relevant. I think this item would be an interesting option for many champions that I mentioned, and still others. I also fully expect that I am overlooking some champions / combinations that would be overly powerful with this item. I don't expect that it will be perfectly balanced as it is, and I would fully expect that Riot would need to do plenty of play-testing in order to find that balance. That is their job, and I would be happy to leave them to it.
Again, I simply think this, or an item similar to this would be an interesting addition to the game, and I am hoping that people will be willing to discuss this with me in a civil and constructive way.
Thanks :)
You know, I don't want them to build
and said item to get a ridiculous amount of damage reduction
this would be a great combo, .. but again, I think it would be better on any of the other champions I mentioned in my post than these three specifically.
?