Rulings
Q1: What does "players can't reduce play costs" mean, exactly?
This effect prevents costs from being reduced when play costs are to be paid. This effect affects both players.
Q2: What does "players can't reduce play costs" effect has activated?
Yes, you can. "Play this card without paying the cost" effects aren't effects that reduce the play cost.
Q3: What does "players can't reduce play costs" effect has activated?
No, play costs can't be reduced. A "players can't reduce play costs" effect isn't an effect that affects cards that activate play-cost-reducing effects, it's an effect that affects players. Therefore, the target players can't reduce play costs.
Q4: What does "players can't reduce play costs" effect has activated?
Yes, DigiXrosing is possible. However, it isn't possible to reduce play costs through DigiXrosing. Therefore, a player can't declare to play a card in a state where its play cost can't be paid.
Data Sources
Lv.3 Otamamon EX7-015 U Rookie | Virus | Amphibian/NSp [Digivolve] Lv.2 w/[NSp] trait: Cost 0 [All Turns] Players can't reduce play costs.
Lv.3 Otamamon EX7-015 U Rookie | Virus | Amphibian/NSp [Digivolve] Lv.2 w/[NSp] trait: Cost 0 [All Turns] Players can't reduce play costs.
Lv.3 Otamamon EX7-015 U Rookie | Virus | Amphibian/NSp [Digivolve] Lv.2 w/[NSp] trait: Cost 0 [All Turns] Players can't reduce play costs.
Lv.3 オタマモン EX7-015 U 成長期 | ウィルス種 | 両生類型/NSp 特徴に「NSp」を持つLv.2:コスト0 【お互いのターン】お互いは支払う登場コストをマイナスできない。