I agree with the importance of SED, as Arekusu said. That and slayer cards should be the main tricks when dealing with elite guards. Furthermore, average SED level should be quite higher than the average during last event, so we should expect to see some nasty HP amounts on those guards now.

As Kotono said, during previous event there were some slayer cards available at N gacha, so F2P players should try to get those free slayer cards asap. After that, SED should be the main stuff for the event.
For those willing to spend some money, then I'd say go for the slayer cards which will be only available at those damn event gachas.

Oh, well, having some puddings always helps.