When this card is Tribute Summoned while you control no Spell/Trap Cards: You can activate this effect; your opponent declares either Continuous Spell or Continuous Trap, then you Set 1 card of that type directly from your Deck. This card gains 300 ATK for each face-up Spell/Trap Card you control. Face-up cards in your Spell & Trap Zone cannot be destroyed by card effects.
I think I solved my case. It because one of my existing monster is Disciple of Ra. Still odd though, since I should be able tribute summon Uranus without using Disciple of Ra (I had Light of Efigy on my board) -_-
This would have been a good card if it lets us declare instead of having our opponent declare the card type.
I would then always combo this card with Shard of Greed.
But thanks to how Konami do the effect when they printed it in real life, Uranus is now one of the worst Planet card.....sure, the manga version just have the ATK gain effect and nothing else, but at least it wasn't reliant on the opponent at all.
Konami should have put The Tripping Mercury instead in Abyss Encounters, not only it is an actually good Planet series card even in the real life print, but also, it's a WATER monster, matching the box it would be in.