25% I guess, some time ago one guy wrote that there are 2 versions of gold ichigo and 1 is before some update and isn't in game anymore but still shows sometime in void although you can't get any bonuses from him, don't know if it is true tho but I doubt you could get 50% attack boost from just one character.
Miken97 replied at 2017-1-29 20:12
25% I guess, some time ago one guy wrote that there are 2 versions of gold ichigo and 1 is before so ...
Same with isshin. And isshin got nerfed. Maybe that's what happened with low life ichigo too. Guess we'll never know since he sucks hara kiris dick anyway
You can see just by adding him to formation then click the confirm button in VR. Hover mouse over the formation button to see if it is 25 or 50 ally bonus.