Dragon Ice

It's an awesome card.

With it in your hand or Graveyard, you can discard a card (including itself, if it's in your hand) to Special Summon it when your opponent Special Summons something.

Not to mention it's a Dragon-type Monster. That gives you access to the amazing Exploder Dragonwing! It basically kills any Lightsworn or Blackwing before damage calculation, preventing them from using Honest or Kalut. It's like Catastor, except it's good against Blackwings. It has some practical uses against Zombie decks, since you can kill off their recruiters outside of battle.

It's also a Water Monster, giving you access to Gungnir, if you're in the OCG. That means you can dump it along with a Hero for Absolute Zero with Future Fusion.

The odd part is that people consider it to be a big threat. In my experience thus far, people go out of their way to get rid of it. I have no idea why, since it's not all that disastrous once it's on the field. It's just 2200 DEF... I suppose that in a Monarch deck, people don't like to let you Special Summon a shield that can be revived multiple times (*cough Treeborn Frog *cough*).

The best thing about Dragon Ice is that it "steals" priority from the opponent when they Special Summon a Monster. Being a Trigger, Dragon Ice's effect is activated in response to a Special Summon, much like how Stumbling triggers when a Monster is Summoned.

It prevents the opponent from using an Ignition effect with priority (like Stumbling), allowing you to chain something like Bottomless Trap Hole or Torrential Tribute to prevent them from getting their effect at all. What's nice about Torrential Tribute is that the field will be cleared before Dragon Ice is Special Summoned.

Oh yeah, and it's kinda helpful against Gladiator Beasts, I suppose. I won't go into that, though, maybe not until Gladiator Beasts come back into power (Starlight Road!).