You choose how many and which creatures and planeswalkers to sacrifice for Devouring Hellion’s ability while it’s entering the battlefield. No player may take actions between the time you choose which permanents to sacrifice and the time Devouring Hellion is on the battlefield with those counters.

If any of the sacrificed permanents have abilities that trigger when Devouring Hellion enters the battlefield (such as that of Kronch Wrangler), those abilities won’t trigger.

If Devouring Hellion somehow enters the battlefield at the same time as another creature or planeswalker, you can’t sacrifice that creature or planeswalker. You may choose only permanents that are already on the battlefield.