Nice team, however I think you're kinda weak to Fire moves, having only one resistance, and a team which is generally weak to the special side. Sun team are going to be a pain to deal with, Venusaur can dismantle your whole team after SR and a Growth boost (Ice Shard deals 85% max, and he will keep itself healthy with Giga Drain to avoid dropping into KO range). Not only that but also Offensive Volcarona is a problem, since if either it carries Giga Drain or LO and Sunlight is up, Jellicent is 2HKO'd and the rest of your team is vaporized without any effort. Also, I feel that Forretress and Donphan's roles are largely redundant: both can spin and set up hazards, while tanking powerful physical hits (and your Lando-T can aid with Intimidate in physical tanking, so...). I suggest
replacing your Volcarona with an Offensive Heatran. Heatran, as the premiere Sun check and Fire absorber, is a pretty big answer to Volcaronas and Fire teams. Since you lack a revenge killer, a
Scarf Heatran could fit nicely on your team, it has the added boon to actually have some chances against Dugtrio and to be a quite underused set, thus carrying a surprise factor.
Heatran

Heatran @ Choice Scarf | Flash Fire
Timid | 4 HP / 252 SpA / 252 Spe
- Overheat
- Flamethrower
- Dragon Pulse / HP Ice
- Earth Power
Also, another concern in your team is the lack of an additional Water resistance. If Jellicent goes down somehow, you're going to be destroyed by Hydro Pump spams or similar strategies. I feel that Donphan and Forretress's roles are pretty much the same, so my suggestion is: ditch Spikes, move Stealth Rock from Donphan to Forretress, and
replace Donphan with a LO Latias. Latias can take Water attacks forever, and can stop dangerous things like Keldeo, provide an additional Sun check, and drop powerful Draco Meteors on things that hope to come in on a more manageable CM version. It also provides an additional immunity to Ground, which is never bad since you actually carry Heatran.
Latias

Latias @ Life Orb | Levitate
Timid | 4 HP / 252 SpA / 252 Spe
- Draco Meteor
- Surf / Psyshock
- HP Fire / Psyshock
- Roost
With these modifications, you gain two hard hitters in Heatran and Latias, that better cover your weaknesses and while lacking set-up abilities, will help to weaken or kill things that may hamper Landorus's sweep.
Hope I helped. Good luck.