It will be the Boss event But maybe Nutaku will make some special changes for this first event. He also didn't reveal if he will use current R/SR's as the assist slayer cards or use the default ones that go with the cards he revealed.

If the daily shop is updated and enabled on Tuesday then people will be able to get a event gacha ticket for just 100p. Regular price is 300 and first spin is also 100. One ticket alone almost guaranteed's your attack will double since the rare slayer appears frequently and the normal is common and available on the pero gacha.

Cheap PeroPuddings almost disappear from the Daily Deal Shop and are all replaces by eGacha Ticket deals.
2Puddings 10p
eGacha 100p
eGacha+6HalfPuddings 300p
eGachax2 500p

He also didn't mention the ranking prizes which give 1Limited SR that is hard to obtain ever again since most of those do not appear on the Pero Gacha. Some cards do go back into the Pero Gacha but most limited will be that...limited and you will rarely ever see them again. Will not be the end of the world if you miss them but they do give you a little extra boost for this Boss slaying event that revolves around your SED. The other events are very differently but this one gives the most rewards since you can spam bosses.