Had a fun little idea, not terribly competitive but something that would at least be interesting to try out. It revolves around bullgryns and cyclops, though you could use demo special weapons teams as well. Basically you use the bullgryns as a shield to advance up to the enemy and them the cyclops move out to detonate in your enemies lines.
This is an expensive thing to run and will prob end up not working too great because of so much pts put into the bullgryns. This really would take some testing to find out the ideal number you would need to get this to work, but lets go with two eight man squads, this gets you to 720pts, yes its a lot, but you can spread your wall out by putting the bullgryns in pairs and then each pair spread out so that they have a 3+ armor save, which is pretty key to keeping them alive. Behind them you can then put 6 cyclops, which will run you 180. This is half your army, so your going to need to help them get across the field with shooting and orders.
If you can get the infiltrate warlord trait, this will help this out a ton, but lets assume you don't. You want the bullgryns at the front with cyclops just behind. After that its simple, you move forward, and either issue the move move move order or forwards for the emperor depending if the bullgryns have targets in range worthy of shooting, most likely don't bother and go for max run distance. If you have enough orders, do the same on the cyclops.
This will also give you a lot of board control as bullgryns can cover a long front and canalize your opponents into moving through corridors that you want them too. This can also cause your opponent to react to this advance and turtle up, keeping him in his deployment zone. A fast and assault heavy army will try and come at you and go through your bullgryns, who are no slouches in combat but will die to deathstar units. This isn't a bad thing, as the cyclops can then charge in to the combat and explode in their midst and as long as you are not facing 2+ save units, they will hurt them quit badly. A marine bike squad is a good example, as even with invis up they will die to the cyclops.
Either way once you get close, the Bullgryns open up and let the cyclops through to explode among your enemies lines. 6 S9 AP3 ordnance large blasts can do a lot of work, especially since you can place them exactly where you want them.
Key to this having a chance at working is having support in your rear to draw some fire as well as eliminate key threats and tarpits that will slow you down. Wyverns will help you destroy chaff and even heavy armored infantry, and using deep striking melta scion squads to eliminate hard to kill armored targets.
Leadership support for the bullgryns is very important, so you can either throw priests in there or take the rampart detachment to make them fearless. Personally the rampart detachment is what I would choose, as you get a lot of buffs for the bullgryns in addition to fearless.
This is more of a silly tactic and prob not too competitive, you could make this work on a smaller scale with a single bullgryn squad and single cyclops unit to hold down a flank and advance that way. This would give you a lot more pts to play with and give better support to the unit. Demo special weapon squads are another option, but are the same price as cyclops squads, so you break even there. They can throw their demo charges, giving them better range, but they also are far more inaccurate reducing their reliability too much for my tastes.
Just something to think about.
GG