Except there is a card called Curiosity already. Maybe Deadly Curiosity ??? Dark Curiosity???

Is this card fine as a hybrid?

It's a bit dubious. If anything the effect is green.

Blue has only got Polymorph effects for the flavour of one creature changing into another, and here that flavour doesn't apply, so I don't think it should be blue. (Blue has occasionally got effects to drop creatures straight onto the battlefield, but either symmetrically as in Show and Tell or Braids, Conjurer Adept, or temporarily as in Aethermage's Touch.)

It's not very black either... dropping creatures straight onto the battlefield is only something black does if they come from a graveyard.

Green, on the other hand, gets this kind of effect frequently: Dramatic Entrance, Elvish Piper, Animal Magnetism, Game Preserve, Hunting Grounds, Hypergenesis, Lure of Prey, Myojin of Life's Web, Oath of Druids, Pattern of Rebirth, Root Elemental, Summoning Trap, Thicket Elemental, Tooth and Nail.

Red dabbles in it sometimes if it's a temporary effect: Sneak Attack, Cauldron Dance, Impromptu Raid, Incandescent Soulstoke, Through the Breach.

(All colours get to do it if it's specific to a colour-aligned creature type: Preeminent Captain, Skirk Drill Sergeant, Goblin Wizard, Seahunter, Skyshroud Poacher, Zirilan of the Claw. Green also gets to do it to lands, white gets to do it to enchantments, and blue gets to do it to artifacts. Other odd unclassifiable versions: Surprise Deployment, Mindwrack Liege.)

So I think this card's effect is only clearly in green. Any other colour is a bit of a stretch, but hybrids in green-blue or green-red would probably be okay.

OK, monogreen seems reasonable. Now let's talk about the cost.

­Summoning Trap and Polymorph are definitely the closest comparison to this. The relevant differences:

• 6 mana instant rare / 4 mana sorcery rare / 3 mana sorcery mythic
• Looks at 7 cards / as many cards as required / as many cards as required
• If multiples found, gives you the choice / picks the first one / picks the first one
• No drawback / Loses you life / Requires a preexisting creature, preferably a token

So Summoning Trap is good if your deck has lots of great creatures that are hard to cast. Polymorph and this card are good if your deck has just a few great creatures that are hard to cast. Obviously this is best if it hits something like Emrakul, the Aeons Torn or Blightsteel Colossus. But unlike Polymorph, if you literally only have 2 creatures in your deck, there's a good chance this will kill you.

If you stuff your deck with a large number of gigantic creatures - Eldrazi, Colossi, and so on - and have no other creatures in there, then this will be quite reliable at getting a stupidly large monster on turn 3, or sometimes turn 2. You'll likely get some of them stuck in your hand, of course. Is that as much of a drawback as Polymorph requiring you to make a token first? I'm not sure, but I think not.

Basically, this card is sort-of-okay in many decks, and possibly extremely good in one or two narrow decks. I'd feel a bit more comfortable if it was at 4 mana, like Polymorph. Even then it'll sometimes be crazily effective (especially since it's in green, the colour of acceleration), but it probably wouldn't warp Standard.