This deck exists for one primary purpose: MAKE LOTS OF GOBLINS! It also exists for a second purpose: MAKE THOSE GOBLINS HIT HARDER! Then you USE THOSE GOBLINS TO ATTACK! It's not a very complicated strategy, BUT IT REQUIRES LOTS OF CAPITAL LETTERS! Red decks aren't about subtlety.
Krenko isn't a powerhouse on his own, but he makes a goblin tribal army grow exponentially. Goblins have the potential to be sacrificed to deal direct damage, and damage can be dealt based on the number of goblins in play. There are even some decent combo opportunities, but the core idea is simply to make lots of goblins and overrun the other players.
The ultimate combo move, which I have managed to use for an epic win only once, involved tapping Krenko to spawn about 20 goblin tokens during the first main phase of the turn. This dealt about 20 damage to one opponent and took him out of the game thanks to the Impact Tremors enchantment. The goblins all had haste thanks to Hammer of Purphoros along with several attack bonuses from various artifacts, so they overran the defenses of the second opponent and took him out of the game during the attack phase. Then in the second main phase, I cast Voracious Dragon and sacrificed as many goblins as I needed to wipe out the third player through that dragon's "Devour" ability.
There are some glaring weaknesses to Krenko's mob. Do you or your creatures have protection from red? I can't always get past that. Can your attackers fly? I can't block that at all. Can you neutralize Krenko? He's the linchpin of this deck, so that slows me down. Can you wipe tokens off the board? There goes my army, and even if I have Boggart Shenanigans in play, it really hurts.
That said, the speed at which this deck can grow an army will completely throw off the plans of other players who need time to get their strategies lined up. It's a fun deck if you like the aesthetics of the Overlord minions. Fling your horde at your foes, and laugh whether they succeed or fail! If you're not attacking, you're not playing an aggro deck properly!