Gnomaterial (MP20-EN050) [2020 Tin of Lost Memories]

If your opponent Special Summons a monster(s) while you control no cards: You can discard this card, then target 1 face-up monster your opponent controls; this turn, that monster cannot be Tributed, or used as material for a Fusion, Synchro, Xyz, or Link Summon. You can only use this effect of "Gnomaterial" once per turn.