I was also intrigued by the Magmortar/Electivire combo when the set was released. I went a little different route than you with it though. I made my deck for speed since I really want to be hitting hard quickly and overwhelm my opponent. While Electivire can be good against Yveltal/Lugia, with just a muscle band Magmortar can one-shot them as well. My version of the deck focuses strictly on Magmortar, and I’m calling it “FIRE & BRIMSTONE”:
4-4 Magmar/Magmortar (FUF)
2-2 Electabuzz/Electivire (FUF)
1 Jirachi EX
1-1 Feebas/Milotic (FLF)
4 Professor Juniper/Sycamore
1 Computer Search
4 Roller Skates
3 Fiery Torch
4 Ultra Ball
1 Pal Pad
3 Muscle Band
2 Training Center
8 Fire Energy
Like I said, the name of the game is speed. The Roller Skates and Fiery Torches let you burn through your deck (pun intended). Since I am never attacking with Electivire, I’ve found that a 2-2 line works just fine, but you can consider a 3-2 line to improve the chance of getting Turn 1 Electabuzz on the bench. The Mewtwo-EX is just there when you need a hard hitter or a wall since we run DCE. Jirachi-EX can be amazing when you need a Blacksmith late game (or a supporter early game). The 1-1 Milotic line is just another way to get energy acceleration if needed late game, but won’t be good against Landorus/Kyurem/Darkrai since Feebas has a measly 30HP (ie: pick your spots to lay down Feebas).
The supporter count is thin I know, but you have lots of item-based draw that helps you out. (Note: Colress could be a good addition as your bench should be well-stocked swarming Magmortar, but I didn’t want to draw Colress in the early game.)
Everything important has a high retreat cost, so 2 switches really help out if you start with Electabuzz or just need to switch to a fresh Magmortar. The Pal Pad helps when you need more Blacksmith late game (you probably have discarded a few with Juniper early game). And finally, this deck needs a counter stadium and I think Training Center works well to help Magmortar survive longer (and you are doing 160-180 damage which should one-shot other evolved pokemon even with the boost in HP).
I’ve had mixed success with this deck online but am waiting until the rotation happens on PTCGO to really give it a thorough testing (It’s not fair to go up against Enhanced Hammers, Accelgor, etc). I usually have no problem setting up by turn 3 at latest with a fully powered Magmortar/Electivire combo.
Bicycle - I’m torn between Roller Skates/Bicycle but have been having better success with Roller Skates
Seismitoad-EX - This helps stall early game sometimes and lets you set up. You can drop some of the speed elements and add 2-3 of these guys.
Garbodor - Sounds good in practice but I can’t find the space really.
Let me know what you think.