In addition to what both the users above has mentioned, I would like to mention that I fail to see any actual focus in this team. From what I can see, you seem to only have checked Smogon for any noteworthy Pokemon and then slapped them together to form a team. That is not really a good idea when it comes to team building, in my opinion.
If you had a certain idea while building this team, please do tell. Anyway...
Shaymin @ Life Orb
Ability: Natural Cure
EVs: 252 SAtk /
4 SDef / 252 Spd
Timid Nature
- Seed Flare
- Earth Power
-
Psychic /
Air Slash / Hidden Power [Ice]
-
Synthesis /
Rest
A recovery move is always helpful, and Shaymin has access to two of them. Synthesis is the most useful but Rest, in conjunction with Shaymin's ability, provides full HP regeneration almost instantly. The last offensive move of choice is completely up to what your team needs. Try out all of them first if you'd like. Also, move those last 4 EVs to SDef in order to deny Porygon and Porygon-Z a free SAtk boost.
Umbreon @ Leftovers
Ability: Synchronize
EVs: 252 HP / 4 Def / 252 SDef
Calm Nature
- Toxic
- Wish
- Protect
- Foul Play
Don't bother with much physical defense, you're not supposed to switch into them as an Umbreon. With the given EVs, any special attacker would be an idiot if it decides to stay in because Toxic + Protect + Foul Play is sure to give them trouble.
Roserade @ Black Sludge
Ability: Natural Cure
EVs: 252 HP / 240 SDef / 16 Spd
Calm Nature
- Giga Drain
- Spikes
- Synthesis
- Sludge Bomb
Roserade is there to set up Spikes and counter things like Swampert.
Although spikes support is really helpful, Roserade has no synergy with your entire team and adds to your already massive Flying-type weakness. I suggest putting Zapdos here, like Boilurn has suggested, because it has great synergy with Umbreon and it checks most, if not all, Flying-types out there.
Zapdos @Leftovers
Nature: Bold
EVs: 248 HP / 236 Def / 24 Spe
~ Discharge/Thunderbolt
~ Roost
~ Hidden Power Flying
~ Heat Wave
Heracross @ Choice Scarf
Ability: Moxie
EVs: 252 Atk / 252 Spd / 4 HP
Adamant Nature
- Close Combat
- Megahorn
- Earthquake
- Stone Edge
looks okay
Sharpedo @
Life Orb
Ability: Speed Boost
EVs: 252 Spd / 252 Atk / 4 SDef
Jolly Nature
-
Protect
- Crunch
- Earthquake
- Waterfall
Life Orb > Choice Band. Protect to rack those Speed boosts.
Blastoise (M) @Leftovers
Nature: Bold/Relaxed
EVs: 252 HP/252 Def/4 SDef
-Scald
-Rapid Spin
-Roar/Dragon Tail
-Foresight/Toxic/Ice Beam
this is basically the set that PlatDude provided
Happy battling!