Here is a list of my item concepts, some may be useless and just niche at best, some may be outrageous.
Ancient Sash [Legendary tier]
- Quick Silver Sash + Needlessly Large Rod
- 45 MR + 80 AP
-Unique Active: Removes all debuffs from your champion, your champion gains 10% Spell Vamp and 35% crowd control reduction for 5 seconds (90 second cooldown)
--- REASONING: APs in general have been underappreciated lately due the changes and progression of the game, burst mages like Veigar, LeBlanc, Annie, etc. have Zhonya's hourglass to wait-out an engage then burst or instagib. DPS Mages like Swain, Cass, Ryze, etc. can do the same, but their damage-output curve is low to high as long as they continue to fight, so if they Zhonya's they may risk their team dying and/or may not be able to clean-up and get focused after Zhonya's active is over and not get a kill in due the nature of DPS mages.
The Warrior's Mug [Legendary tier]
- 35 MR + 45 AD
- Chalice of Harmony + Pickaxe
- Unique Passive - Mana Font: Increases your mana regeneration by 1% per 1% mana you are missing.
- Unique Passive - Based on the damage dealt to champions, you gain 5% of the damage dealt as mana.
--- REASONING: It bothers me that there isn't an AD version of Chalice yet. And yeah, this item is more specific to AD casters and allowing more counter play.
Cursed Impaler [Mythical Tier]
- Giant's Belt + Atma's Impaler
- 400 HP + 55 ARM + 20% CRIT CHANCE
- Unique Passive - Bold Force: You gain attack damage equal to 1.5% of your maximum health.
- Unique Passive - For each 5% percent of health missing, you gain 1% additional critical strike chance.
--- REASONING: Atma's has potentials to be a force to fear (especially in this defense meta), but only certain champions can utilize the most of it. People complain on how attack damage bonus is rather weak, I think it's powerful and I thought of an item that could definitely see use today. Also, game modes exist that don't have Warmogs (looks at Dominion).
These are just some I came up with. Whether you think they are overpowered or just useless won't matter to me as they're not part of the game.