I've got a few so let's get this out the way
Well, in the show Goku was able to train himself in Kaio-Ken until he didn't feel any after effects from it. This is seen from the show when in the Saiyan Saga Goku's max was x3, and it destroyed his body, while in the Freiza Saga he went x20 and felt no after effects.
So what I have planned, it that while learning Kaio-Ken, you can decrease an completely get rid of some the cons (not the turn limit however). Basically, when you learn the Kaio-Ken above your current max, the cons after in half, and the level above that, the cons disappear.
For example, if you have Kaio-Ken and you Learn Kaio-Ken x20, Kaio-Ken has no cons, and Kaio-Ken x10 has halved cons.
Okay, all the other Legendaries have at least one other boost rather than being a transformation or boosting the others. I mean, it's actually the worst Legendary there, and nobody really wants to pick it.
In this suggestion, I recommend giving LSSJ extra resistance from all attacks and extra damage output from physical attacks. I mean, look at Broly. When he turned into his LSSJ form, his energy attacks weren't really what everyone worried about, it was more worry towards his physical strength and his ability to tank through attacks like nothing.
The resistance gain would only be 25% and the increase in physical damage is only 15%.
- Saiyan Skills
Alright, I got this one from Goku (man, a lot of him today huh?), well saiyans get stronger while they fight and I realized that this is a seperate trait from Zenkai (or could be added to it). I was thinking it could replace the +50k HP, or be added on to Zenkai.
This one isn't as well planned as the others because it's not very well explained. So I was just thinking of a small stat gain of .1 during each person's turn as a start, so it would 10 turns till you get a stat gain of 1 completely.