About SubCM Kyogre: If it's an issue, you can run SpDef Lugia to take on it better (Modest Max SAtk+ Surf does 42% max, Ice Beam does less, Thunder does about 47% max. But you probably have a better shot dealing with Thunder variants anyways due to sun). CM up on its face, Whirlwind, and let it suffocate from Toxic Spikes later on. Hopefully by the end of the game you have weakened it sufficiently, or still have most of your team members to hopefully stall it out.
Honestly the biggest weakness to this team is entry hazards. It's not difficult to set up hazards against your team (Forry and Ferro set up on at least half the team. Forry is especially dangerous as it puts you into a checkmate position - if you try to spinblock it, it gets 2-3 layers. Skarmory isn't enjoyable to face either, since it's immune to Spikes, and can Taunt Forretress and switch to a spinblocker to prevent it from doing anything). Toxic Spikes isn't as annoying, but Tentacruel's TS absorption is annoying, and Toxic Spikes will force Giratina/Blissey to heal more. Not much you can do about that, however. Giratina-O > Giratina helps with the Spikes issue greatly, but then you have to deal with the Ho-Oh issues. Giratina-O's 4 moveslot syndrome doesn't help much either (you're going to need Dragon Tail/Shadow Sneak/HP Fire/Will-o-Wisp to maximize your coverage against most threats, and I'm not sure how you'll like losing Draco Meteor). On the bright side, though, Giratina-O helps make Mewtwo much more manageable.
I suppose if you do go with Giratina-O, you can swap Lugia for something else that covers up Ho-Oh better. Unfortunately, I don't know exactly what. Rock Arceus could work but you'll have to play more carefully against SubCM Kyogre. Putting Kyogre on that slot can sort of help with Ho-Oh and CM Dark Arceus, somewhat, as well as helping against Ground Arceus and freeing up the Will-O-Wisp slot... But this just turns your team into my Gen 4 stall team ._.
The other threat to watch out for is the surprise Rapid Spin. This team operates very heavily on entry hazards and an unsuspecting Rapid Spin Cloyster/Kabutops can turn the tide around. Beware.
I apologize for the long train of thought.
Also, use Gyro Ball on Forretress. Gliscor is annoying but with Gyro Ball you have a better fighting chance against SubNP Darkrai. You can also leave a dent on Mewtwo, which is helpful. Gyro Ball is also still strong enough to prevent Cloyster from setting up on it (it hits a full 150 BP after a Shell Smash).
I hope you don't fight the extremely odd speedy (by that I mean faster than Lugia) Whirlwind Ho-Oh (it's something I've used before in Gen 4 to break through Giratina-A stall). With a bit of entry hazards it can completely flatten your team without blinking. To make your life miserable, it also roasts the only two things that could stop its sweep, Forretress and Blissey (the former could spin and the latter could Toxic).
Honestly the biggest weakness to this team is entry hazards. It's not difficult to set up hazards against your team (Forry and Ferro set up on at least half the team. Forry is especially dangerous as it puts you into a checkmate position - if you try to spinblock it, it gets 2-3 layers. Skarmory isn't enjoyable to face either, since it's immune to Spikes, and can Taunt Forretress and switch to a spinblocker to prevent it from doing anything). Toxic Spikes isn't as annoying, but Tentacruel's TS absorption is annoying, and Toxic Spikes will force Giratina/Blissey to heal more. Not much you can do about that, however. Giratina-O > Giratina helps with the Spikes issue greatly, but then you have to deal with the Ho-Oh issues. Giratina-O's 4 moveslot syndrome doesn't help much either (you're going to need Dragon Tail/Shadow Sneak/HP Fire/Will-o-Wisp to maximize your coverage against most threats, and I'm not sure how you'll like losing Draco Meteor). On the bright side, though, Giratina-O helps make Mewtwo much more manageable.
I suppose if you do go with Giratina-O, you can swap Lugia for something else that covers up Ho-Oh better. Unfortunately, I don't know exactly what. Rock Arceus could work but you'll have to play more carefully against SubCM Kyogre. Putting Kyogre on that slot can sort of help with Ho-Oh and CM Dark Arceus, somewhat, as well as helping against Ground Arceus and freeing up the Will-O-Wisp slot... But this just turns your team into my Gen 4 stall team ._.
The other threat to watch out for is the surprise Rapid Spin. This team operates very heavily on entry hazards and an unsuspecting Rapid Spin Cloyster/Kabutops can turn the tide around. Beware.
I apologize for the long train of thought.
Also, use Gyro Ball on Forretress. Gliscor is annoying but with Gyro Ball you have a better fighting chance against SubNP Darkrai. You can also leave a dent on Mewtwo, which is helpful. Gyro Ball is also still strong enough to prevent Cloyster from setting up on it (it hits a full 150 BP after a Shell Smash).
I hope you don't fight the extremely odd speedy (by that I mean faster than Lugia) Whirlwind Ho-Oh (it's something I've used before in Gen 4 to break through Giratina-A stall). With a bit of entry hazards it can completely flatten your team without blinking. To make your life miserable, it also roasts the only two things that could stop its sweep, Forretress and Blissey (the former could spin and the latter could Toxic).
