Sit on the dome, frog those legs out.
Balance through your core, not your arms, and keep the dome steady.
Frog kicks on the dome are a tuck-and-extend rhythm, knees pull to your chest, then both legs shoot straight out while your trunk balances the whole show on an unstable dome. The extension is the hard part, long legs pull your centre of gravity away from you and the abs have to both hold the lean-back and reel the knees back in. It earns its place as lower-ab focused work that trains balance and compression in the same breath.
Frog kicks move both legs together, tuck in, kick out, while bicycles alternate one leg at a time. The double-leg extension makes frog kicks a bigger single hit to the core, bicycles spread the load into a longer rhythm.
Extending both legs pushes your weight away from your base, which is the peak demand on your abs and your balance simultaneously. If you collapse there, extend the legs higher rather than straight out, and lower them as you get stronger.
No, the set lives in the unbroken tension. Tuck, extend, and tuck again without touching down, when you can no longer keep the feet up, the set is over, not the form.
