Here's my serious rating.
Yes, Arceus, the so-called God of Pokemon. Base 120 stats everywhere is nothing to joke about, and with Multitype and its massive move-lake, its versatility is just crazy. And you have to admit, Swords Dance + ExtremeSpeed is deadly. It's the one Pokemon banned on the Ubers ladder on Shoddy, and for good reason.
With Base 125 Speed and base 135 Sp. Attack, as well as the second-most accurate sleep move (Dark Void), Darkrai can be a nightmare. It'll put you to sleep, and Bad Dreams will hurt you over turns. This kills any Sashes. As the foe dozes or switches, Darkrai can set up Nasty Plot, raising its Sp. Attack to frightening heights. If you come across this thing, I hope you're a light sleeper.
The king of Water-type Pokemon, no doubt. When it comes in, Drizzle will cause rain, boosting the power of its already-scary Water-type attacks. A Choice Scarf set will hammer your foe hard and fast. Did I mention hard? If it uses Water Spout at full HP, considering rain, STAB, Kyogre's massive base 150 Sp. Attack, and Water Spout's sheer power... may Arceus have mercy on your foes.
The most revered wall in all of Pokemon. It competes with Giratina, but look at Lugia's base 106 HP, 130 Defense, and 154 Sp. Defense. Without setup or a critical hit, there's virtually no chance of tearing it down in one hit. Base 110 Speed is nothing to underestimate, either. Roost can keep it alive and kill some weaknesses for a turn. It can PP stall with Pressure, even! You'd better be ready to slam this thing hard, and I mean hard. You'll need to.
And finally, number 5.
5. Deoxys (Attack Forme)
With an outright savage base 180 Attack and Sp. Attack, as well as a blazing base 150 Speed, this thing is capable of ripping a gaping hole in just about any team. So why is it number 5? Despite its sheer offensive power, it has Carvanha-level durability. Even resisted hits will hurt. A Focus Sash is its only sure way to survive, and Stealth Rock/Spikes can ruin that. But don't underestimate this thing at all. If you do, you'll live to regret it... if you come out alive.