Detaching 1 Xyz Material from this card is the cost to activate this effect.[1]
If "Evilswarm Thanatos" is in face-down Defense Position when its effect resolves, the effect "this face-up card is unaffected by other monster effects this turn" is not applied. If "Evilswarm Thanatos" is changed to face-down Defense Position after applying its effect, the effect "this face-up card is unaffected by other monster effects this turn" stops being applied.[1]