>>39852617Could also just rework the existing one.
Slow Start halving speed and attack could just be explicated to it being -2 on entry, and then at the end of every turn it gets +1 in both of those stats. Think of it like Speed Boost, but also effecting attack. A passive Dragon Dance.
Something like that I feel would be a little on the overpowered side, but not too bad considering it doesn't get protect or rest, and is still consistent with Regigigas lore.