If your opponent Special Summons a monster (except during the Damage Step): You can target 1 of your banished "Metaphys" monsters; Special Summon it, but banish it during the End Phase of the next turn. If your other "Metaphys" card in its owner's possession is banished while this card is already face-up in your Spell & Trap Zone: You can target 1 card your opponent controls; banish it. You can only use each effect of "Metaphys Dimension" once per turn.
Monster you Special Summoned is banished during the next turn’s End Phase.
Can only banish your opponent’s monster when your Metaphys monster is banished.
This card’s first effect works to trigger it’s second effect. When your opponent Special Summons a monster, you also get to Special Summon a Banished Metaphys monster. When that Metaphys monster is banished during the next turn’s End Phase it drags your opponent’s monster down with it.
Here are the monsters you can Special Summon from the banish zone with Metaphys Dimension's effect. These monsters will trigger Metaphys Dimension's effect when they are banished.
So I’ve been noticing that when I have banished Metaphys monsters and my opponent summons a monster outside of the damage step, it does not prompt me to special summon my banished monster. Is this a (known) bug or am I misunderstanding how the card works?
I'm just here to remind you that this Trap Card does not trigger the effects of your "Metaphys" monsters because they need to be Special Summoned by the effect of a "Metaphys" monster. The second part of the effect is fine and this is searchable via Metaphys Nephthys, but it might be a bit too slow.