Thoughts on a "Merge" mechanic

While playing some Majora's Mask 3D, I got the idea for a Champion mechanic whereby a support Champion (i.e. a sentient mask) can merge with a target allied Champion to drastically increase that ally's bonus stats (i.e. bonus AD, bonus AR, etc.; this means you won't give an ADC huge resists, or give a tank huge damage). The catch? Merging with said ally has a price: if your ally dies while you are merged with him/her, you either take huge damage or die alongside them. Of course, to avoid having someone grief you once you merge with them, you can cancel the merger at a moment's notice.

But I'd like to know if such a mechanic might be deemed toxic, anti-fun, or just plain wrong.