If more items had actives.

This could be a fun RGM!

Numbers obviously out of my ass.

Only top tier items that don't already have one:

Abyssal: creates a circle poisoned mist which lowers the MR of enemies inside of it, disappears after X seconds.

Ardent: your next heal / shield is 10+X(1?)*LVL% more effective.

Banshee's: Consumes your shield and gives it to an ally, the shield returns to you after a delay. (shield must be up for either transfer to occur)

Berserker's: You enrage and your basic attacks deal X+A*lvl true dmg for 1/1.5/2 seconds.

Mobys: Puts down an aoe speed boost zone in the targeted location (scuttle boost, only one per champion can be present on the map).

Swiftys: Can't be slowed for 2 seconds.

Dead Man's: Marks an enemy in range, your speed boost is doubled when running towards her (any none-ally unit).

Death's Dance: For 1 second you take 20% less dmg, after a delay 20% of the dmg taken during the active is restored as health.

Duskblade: For 1.5 second activate "death's search". If you kill an enemy champion while death's search is active the cooldown of Duskblade is refunded.

Reaver: Your next ability deals increased dmg.

Frozen Heart: The next target that auto attacks you is frozen in place for one second (rooted), the effect lasts 1 second.

Frozen Mallet Throws the Mallet into targeted location, creating a slowing zone, your basic attacks don't apply the passive if the mallet isn't on you, you can recall the mallet (does not refund the CD but the passive now applies).

Guardian Angel: Toggle the passive.

Rageblade: Your next attack applies on hits 3 times.

Iceborn: For 2 seconds gain a boost of armor, slow AOE is doubled (after the armor is applied).

Infinity: Spawns a clone in the targeted location that will attack the closest enemy (champion-> objective-> minion) for 2 seconds (50% dmg, the clone can't move)

Lucidity: Your next basic ability will have its CD halved.

Liandry's: For 2 seconds the burn applied maximum health dmg instead of current health dmg.

Lich: Applies an AA reset, your next basic ability deals additional dmg.

Dominik's: Applies a bond to an ally champion, consecutive attacks against the same target apply X armor reduction up to Y. (one stack is applied once both champions attack the target once)

Luden's:
> Unique: Deals 15% of target champion's maximum health in magic damage and applies the debuff, Doom. Doom amplifies all magic damage that champion takes by 20% for 4 seconds. 90 second cooldown (750 range).

;)

Manamuna: toggle effect Attack damage bonus x1.5 (to 3%), mana consume x2 (to 4%)

Mejai's: Obtain 10 stacks for 3 seconds.

Mercury's: For .5s apply a buff that will parry the next spell.

Morello's: Drophack enemy Irelia. When she reconnects she spawns in your fountain instead of the enemy fountain. Ahem I mean ... Sends out an expanding wave of energy that grievousness wounds in an expanding circle around you.

Reminder: Marks an enemy champion, if you kill the enemy then your basic attacks pierce a % of their armor. Stacks up to 3 times, if the mark is applied to another champion then all stacks on marked champions are reduced to 1.

Nashor's: Gives a short burst of AS, basic attacks and abbilites apply an armor and mr reduction - 5 per stack up to 25.

Tabis: For 0.5 s applies a buff that lets you dodge the next basic attack.

Dcap: Spawns a ghost of the last enemy champion you killed, the ghost cannot move but blinks to the end location of your spells and auto attack the closest enemy champion, X% of enemy champion's damage Y duration.

Fire cannon: Fires a protective into a target location, upon explosion creates scorched earth that grounds units in the area (I'd say 3x-4x smaller than maiasma)

Roa: Applies a 40% slow to yourself for 2 seconds, gain 20% ap for the duration.

Runan's: For 2 seconds all the bolts that would hit separate targets are instead focused on your primary target.

Rylai's: Leave behind a path of ice as you move, gain a brief speed boost.

Sorcs: Curses a small area on the ground, champions within the aread take increased dmg.

Visage: Spawns a wolf spirit that will follow the closest enemy champion for 10s, idle for 45s. If the wolf spirit catches up to the enemy it chases it will mark them giving you vision of the enemy an increased MS towards the target.

Stattik: Sends out a bolt of electricity that passes through X number of enemies dealing X magic dmg and interrupting channels.

Sterak's: Belittle an enemy, decreasing their size and lowering their MS for a short period of time.

Sunfire: Create a supernova explosion around you dealing X magic damage (increased dmg to minions).

Cleaver: For 3 seconds your basic attacks cleave in a crescent aoe in front of you

Bloodthirstier: Locks the obtained shield for X seconds.

Thornmail: Create a vine of metal thorns in front of you in a line that applies a slow but is destroyed when stepped on (a chain of lets say 5 thorn sections, maybe ez w range or so.

Trinity: Become invulnerable to damage if spawned in enemy fountain. Ahem I mean... Perform a small dash.

Void: After a delay summons a black hole in a large area, for 2 seconds all champions within the range are grounded.

Warmog's: for 2 seconds gain 76 MR and an 8% speed boost.