Here, in this guide, I will tell you about combined items and highlight the Strongest of them. So if you will build these items, the most likely that you will win the game!
I'll divide these items by tiers, from the God-Tier (S-Tier) to the B-Tier. And speak firstly about the strongest of them. All boosters from the https://tft-boosting.com perfectly know all of them, so if you want to climb the ladder as efficiently as them, you would better learn this too.
S-Tier combined items in TFT
Combined items are created by placing two basic items in the champion. After a 9.14 update many items were rebalanced, so let's start my little Tier list.
Cursed Blade (Negatron Cloak plus Recurve Bow)
Attack have a chance to decrease level of the champion by 1. Champions could be decreased even down to the 0 star level! Equipe some Gunslingers with this item and watch gow multiple champions are de-ranked.
Force of Nature (2x Spatula)
Force of Nature increase team size by one. Unit with this item champion could be placed on the board even if the champions limit is already reached. It opens a lot of doors in creating various TFT synergies.
Guinsoo's Rageblade (Recurve Bow plus Needlessly Large Rod)
Item that endlessly stack 4% attack speed per attack. The League of Legends have the same item, and it works perfectly in TFT on a carries like Draven and etc.
Ionic Spark (Negatron Cloak plus Needlessly Large Rod)
When enemy champions cast a spell, they receive 200 damage. Incredible item that will partially counter every team. The damage is true, so it cannot be decreased, and champions with spammy abilities (like Lucian or Twisted Fate) will suffer a lot.
Rapid Firecannon (2x Recurve Bow)
The item that greatly expands the range of champion's attack. Also this item gives a lot of attack speed and fully counters Yordles (attacks cannot miss), just how it could be bad?
A-Tier combined items in TFT
A-tier items could be slightly situational, but still they are extreme good and could bring a lot of advantages over an enemy.
Bloodthirster (Negatron Cloak plus B.F. Sword)
Almost perfect item for all right-clicker (champions with the insane auto attacks). Champions like Fiora or Draven love this item, with this one they could tank much more due to the increased durability.
Darkin (Tear of the Goddess plus Spatula)
With the increased popularity of Demons, how this item could be bad? Especially taking into the account the Demons do not has any good carry, so you could add one and complete the synergy.
Dragon's Claw (2x Negatron Cloak)
The must have item if you are facing six sorcerers. Almost fully neglects the incoming magic damage (champion is gained with 83% of magic resistance), so give it to your best hard carry and look how mages are trying to kill him.
Frozen Heart (Tear of the Goddess plus Chain Vest)
As you already know, the Attack Speed has the enormous value in TFT, and this item decreases it on the enemies. This is a solid A-Tier item that also gives additional mana from the start, so do not hesitate to give it to the casters, especially if opponents has Assassins.
Frozen Mallet (Spatula plus Giant's Belt)
Glacials are still extremely strong composition, so why don't turn some champion with the insane attack speed into a Glacial to give him a chance to keep someone in stun forever?
Guardian Angel (Chain Vest plus B.F. Sword)
Interesting item, but you need to use it right. In the worst case, you will have a died champion with the two components that could be used for another cool artifact. But in the best case it could be used on the Gnar (for example) to make sure that he will use his ultimate ability!
Hextech Gunblade (Needlessly Large Rod plus B.F. Sword)
Magical lifesteal that will heal for 25% of all damage done. Champions with the high AoE ultimates, like Akali, Brand, or Aurelion Sol would benefit from it the most.