Zilean's ultimate can get lowered to 28 seconds
When you combine The Ultimate Hat/Transcendence/Cosmic Insight and only 2 CDR items, being Morellos and Lucidity Boots, you get a guardian's angel every 30 seconds.
I don't even have to go into detail to explain just why and how this isn't okay...but yeah. This? This is just... I don't even have words. You can actually bait out the zilean ult, press on the attack and push, then in only 30 seconds, it's already back up.
If you're in a teamfight that lasts a single minute, you can use your ultimate 3 times on a target or others. This means that theoretically you're not fighting a 5v5, you're fighting an 8v5.
I'm not gonna say it's broken or overpowered, but I'm just gonna let you guys decide if this is okay or not.

i can have
on a less than minute cd