This is my Death Theme team, it's pretty good. It has a bit of trouble with noobs using skarm/bliss.
Gengar (M) @ Leftovers ** Death's Remains
Trait: Levitate
EVs: 252 Spd / 252 SAtk / 6 SDef
Modest Nature (+SAtk, -Atk)
- Fire Punch
- Giga Drain
- Ice Punch
- Thunderbolt
You could try Psychic over something, maybe Fire Punch if it doesn't help much.
Steelix (M) @ Choice Band ** Death's Gaurd
Trait: Rock Head
EVs: 252 Atk / 128 Def / 128 SDef
Adamant Nature (+Atk, -SAtk)
- Earthquake
- Explosion
- Hidden Power [Bug]
- Rock Slide
Steelix has plenty of Defense, so take all the EVs out of Defense and put 120 into HP, and the rest into Special Defense.
Houndoom (M) @ White Herb ** Death By Arson
Trait: Flash Fire
EVs: 252 Spd / 252 SAtk / 6 SDef
Modest Nature (+SAtk, -Atk)
- Crunch
- Flamethrower
- Overheat
- Will-O-Wisp
Pursuit over Overheat, give him Lefties. You could also try a subbing set with Petaya. As far as the EVs, Timid nature, 252 spd, 176 satk, the rest into either sdef or HP.
Milotic (F) @ Lum Berry ** DeathbyDrowning
Trait: Marvel Scale
EVs: 32 HP / 128 Def / 220 SAtk / 128 SDef
Modest Nature (+SAtk, -Atk)
- Ice Beam
- Recover
- Surf
- Toxic
With Milo's trait, take out the Lum Berry and give her Lefties. You have enough Special Sweepers, so I'll suggest a different EV layout.
Bold Nature, 156 HP/252 Def/8 Spd/26 SAtk/68 SDef
The moveset itself is fine.
Scyther (M) @ Salac Berry ** Grim Reaper
Trait: Swarm
EVs: 252 Atk / 252 Spd / 6 SDef
Adamant Nature (+Atk, -SAtk)
- Hidden Power [Ghost]
- Reversal
- Substitute
- Swords Dance
I suggest HP Bug over Ghost. If he doesn't have exactly 1HP at the last Sub, I'd change the EVs a bit.
Jirachi @ Leftovers ** Death's Destiny
Trait: Serene Grace
EVs: 252 Atk / 128 Def / 128 SDef
Adamant Nature (+Atk, -SAtk)
- Body Slam
- Cosmic Power
- Shadow Ball
- Substitute
I've never used a Phys Jirachi, so I'm not quite sure about the EVs.
Adamant Nature, 84 HP/248 Atk/176 Def
Try that EV spread and if it doesn't work, go back to the original one.
Oh and, try Wish over something. It will really help out Jira and the other Pokes on your team.