After a while of researching, a Redditor u/Semprosius figured out a way to overcome the URF effect with a 90% cooldown reduction.
“TIL you can have up to 89.164% CD Reduction on your ultimate in a Summoner’s Rift game. This means that you can use you R almost twice as often as in URF.”
To achieve 89.164% ult cdr, you need:
- Ornn (to have an upgraded Mythic item)
- Ultimate Hunter (25% Ultimate CDR)
- Transcendence (10 Ability Haste)
- Ability haste rune shard (8 Ability Haste)
- Draktharr’s Shadowcarver or Liandry’s Lament or Starcaster Starcaster (25 Ability Haste + 25 from Mythic Bonus)
- Vigilant Wardstone (40 Ability Haste)
- Cosmic Drive (30 Ability Haste)
- Navori Quickblades (30 Ability Haste)
- Black Cleaver (25 Ability Haste)
- a 20 Ability Haste Item (e.g. Zeke’s Convergence)
- Blue Buff (10 Ability Haste)
- 4 Cloud Drakes (4*10% Ultimate CDR)
This gives a total of 10+8+(25+25)+40+30+30+25+20+10 = 223 Ability haste. Even though the ingame tool tip says that Cloud Drakes give 10 Ultimate Ability Haste, they actually give 10% Ultimate CDR (according to wiki and my tests). Also, the CDR from Ultimate Hunter and from the Cloud Drakes stacks additively (according to wiki and my tests).
So, in total, our cooldown is reduced by 1 – (100/(100+223))*(1-(0.25+0.4)) = 0.89164… = 89.164%.
To show that this is indeed correct, I tested it in practice tool. Unfortunately, I have 5 Ability Haste less, because I can’t have an Ornn on my team. This means, that I only have 88.99…% CDR. I tested it with Morgana, who has 100s cooldown on level 16 ultimate. In this screenshot, you can see that she has 11.01s cooldown, which confirms that her cooldown is reduced by 88.99%. Proof
URF only gives you 80% cdr (but on all abilities). So Morgana’s R would have a cooldown of 20s.
Looking at the above conditions, we can see that possessing nearly 90% of the ultimate cooldown is extremely difficult, even impossible. The reason is that items that provide a lot of ability haste often have stats that don’t interact with each other. Nobody would buy Cosmic Drive, which increases AP with AD items like Black Cleaver or Navori Quickblade.
Luckily, Riot left the ability haste stats on various item so it would be extremely difficult to stack this stat up too highly. It’s hard to imagine what LoL would be like if a champion had nearly 90% of the ultimate cooldown.
Information From: Reddit