Need help with a team!

I love my team the way it is, but unfortunately it's useless against things like Mega Venusaur and Cresselia.
Can someone recommend something that can help out with that majorly?

And this is for the actual games, so I don't care about any of those dumb Smogon rules or whatever.

My team so far is:

Archeops with Focus Sash
Attack & Speed EVs & Jolly Nature
Moves:
Quick Guard (for those Mega Kanga's)
Knock Off
Rock Slide
Aerial Ace

Spinda with Chople Berry or Mental Herb
(NOT getting ride of Spinda. It makes things like Mawile useless and gets rid of Archeops' Defeatist)
HP & mixed defences EVs, Jolly Nature
Ability is Contrary
Moves:
Fake Out
Encore
Skill Swap
Fake Tears

Ambipom with Normal Gem
Attack & Speed EVs,Adamant Nature
Ability is Technician
Moves:
Double Hit
Revenge
Acrobatics
U-Turn

Mew with Kasib/Colbur Berry (mainly used only in doubles, where this set makes it pretty awesome)
EVs: Maximum Special Attack, enough Speed to make its speed at level 50 186, the rest in Attack.
Modest nature
Moves:
Psychic
Frost Breath
Swords Dance
Flame Charge

Umbreon with Leftovers
Attack and Speed EVs (my main way to beat Cresselia, killing it in two hits)
Synchronise ability
Moves:
Pursuit
Screech
Payback
Moonlight

Golem with Weakness Policy (NOT getting rid of this one)
Attack & Speed EVs
Sturdy ability
Moves:
Rock Blast
Iron Head
Earthquake
Automise


If anyone has any ideas on how to make this team better-fit for killing those awfully-defencive Pokemon (mainly Cresselia and Mega-Venusaur, and of course more that I can't think of at the moment) I'd really appreciate it.

But keep in mind that I started over so I have only my Bank Pokemon and a few items a friend traded me before also starting over. So no mega-stones or Battle Resort items other than the above mentioned for a while.

Put something with Taunt/Substitute+Setup move on your team and your problems with stallers should be (almost) resolved. Also, it might be a good idea, to explain, how your team works; you know, "as a team"

Out of curiosity, is this team for singles or doubles?

Assuming singles:

Specially defensive Gliscor or bulky Talonflame can handle Mega Venusaur and Cresselia, since it can either use Taunt to stop them from setting up, or set up Swords Dance in their faces and eventually overwhelm them. Either should go over Archeops, as while it has good stats, its ability cripples it when it's at half health or less:

Gliscor:
-Swords Dance
-Earthquake
-Knock Off/Facade
-Roost
Nature: Careful
EVs: 244 HP/8 Def/200 SDef/56 Spe
Item: Toxic Orb
Ability: Poison Heal

or
-Earthquake/Knock Off
-Taunt
-Toxic
-Roost
Nature: Careful
EVs: 244 HP/8 Def/200 SDef/56 Spe
Item: Toxic Orb
Ability: Poison Heal

Talonflame:
-Swords Dance
-Brave Bird/Acrobatics
-Will-o-Wisp/Taunt
-Roost
Nature: Adamant
EVs: 248 HP/252 Atk/8 Spe
Item: Leftovers/none
Ability: Gale Wings

or
-Brave Bird/Acrobatics
-Bulk Up/Taunt
-Will-o-Wisp/Taunt
-Roost
Nature: Careful
EVs: 248 HP/252 SDef/8 Spe
Item: Leftovers/none
Ability: Gale Wings

Just saying, Umbreon's offensive presence is utterly pathetic, meaning it must rely on Foul Play as its main attack (this attack uses the target's Attack instead of the user's to calculate damage). Given Cresselia's massive defenses, this is what'll happen:

252 Atk Umbreon Pursuit vs. -2 252 HP / 252+ Def Cresselia: 108-128 (24.3 - 28.8%) -- possible 5HKO after Leftovers recovery

Yes, it's possible that Cresselia will be OHKOed at -6 Defense if it switches, but smart opponents can switch out Cresselia before that happens.

Spinda's terrible stats hinder it in any format possible. Just putting that out there.

Revenge has negative priority, and this doesn't work well with Ambipom's frailty.

Mew has 100 base stats all-round, so the absolute maximum Speed it can get is 167 with a +Speed nature (unless you factor in the Flame Charge boost). Even then, Mew is more effective at support roles, IMO, since there are other Psychic Pokemon that can do offensive roles better.

I know you may not care about Smogon rules, but this is still worth a read, IMO: https://www.smogon.com/smog/issue37/bad-to-the-core

Skye_Blue said:

Mew with Kasib/Colbur Berry (mainly used only in doubles, where this set makes it pretty awesome)
EVs: Maximum Special Attack, enough Speed to make its speed at level 50 186, the rest in Attack.
Modest nature
Moves:
Psychic
Frost Breath
Swords Dance
Flame Charge

Click to expand...

I don't really understand this Mew set, and I'm a Doubles player. First and foremost, the most speed Mew can get at level 50 is 167, and that's with a +Speed nature. If you gave it Nasty Plot instead of Swords Dance and just let it be a Modest Mew instead of jerry-rigging it into a "Mixed" set I think you'd be doing yourself a world of favors.

+2 252+ SpA Mew Psychic vs. 252 HP / 52 SpD Mega Venusaur: 230-272 (122.9 - 145.4%) -- guaranteed OHKO

You can run any number of coverage moves to make it work, I'd recommend Shadow Ball and Ice Beam.