I always wanted to try this Eggy set as a lure for many fire type counters and let the fire types burn everything down afterwards:
Exeggutor @ Heat Rock
-Sunny Day
-Sleep Powder
-Wood Hammer
-Explosion
Jolly 252Atk/252Spd/4HP
Three rather common pokemon who have a high chance of switching in on Eggy who greatly hinder fire type pokemon: Tyranitar, Heatran, and Blissey.
Ideally, this set would do three things: Sleep Heatran, Wood Hammer Tyranitar for the near OHKO [289 Atk vs 230 Def & 404 HP (120 base power): 324-384 (80.2%-95.05%)], and Explode on Blissey. However under most circumstances this set will not do all three, but whatever, it always seemed like a fun set to use. Obviously you would Sunny Day first turn, reaching a speed stat of 458, outspeeding plenty of Choice Scarfers (Gengar and Azelf don't run max speed now that Deoxys-S is gone, right?), but barely missing Jolly Ninjask (Ninjask is dumb anyway). From there, depending on who was sent out, act accordingly. Hell, if they send out a Blissey, sleep it, and sleep again a turn right after. Explode should come after you've done something else. Don't Explode right away. Nevertheless, it grants you a good kill (most likely) and a free switch (to your Heatran or whatever) to your awesome fire type.
Looking at Eggy's attacking stats, one would say "just use Grass Knot because we all know how shitty Solarbeam is already, and Eggy has base 125 (!!!) special attack, as opposed to its base 95 (not bad) attack." The two things that Wood Hammer is hitting hard is Blissey and Tyranitar, both of which take laughable (when compared to Wood Hammer) damage from special attacks. Yes, if you do use Sunny Day on the Tar switch in its boost will be nullified, but the use of only physical attacks allows Eggy to max its attack stat, and it wouldn't have to split EVs. Tyranitar also would never INITIALLY switch in to Eggy, because it's, well, a grass type, but it will happily switch in once it suspects it's going to fire off a Solarbeam. Wood Hammer is also great on Blissey if you must [289 Atk vs 130 Def & 714 HP (max/max) (120 base power): 288 - 339 (40.34% - 47.48%)], dealing a comfortable 2HKO to the most common one nowadays (Obi's special defensive one).
So yeah, pair it with Heatran or any other usable fire type in OU (Moltres?) and blast away with Sunny Day boosted Fire Blasts and have fun, most likely with Hidden Power [Grass] to clear bulky waters. These coming months are going to be very cold, and Eggy is just the thing to use to brighten up your day.