>>44451781Pressure.
Or if we're stuck with Slow Start then make it actually good. By that I mean have Regigigas start at -2 in Atk and Speed on switch in (as it already effectively does) and then at the end of each turn have it gain +1 to Atk and Speed, up to the normal max of +6. Essentially a passive Dragon Dance at the end of each turn while starting at -2 on switch in.
Is that broken? Yes. But it should be. It is Regigigas, and once it gets going it should be a genuine force of nature.