An interesting Trick Room team. However, Taunt screws your primary strategy. Your fastest Pokemon is your Lucario which has a mere 90 base speed so anything that is faster than 90 base speed could be considered a threat.
Donphan should run an Relaxed Nature so that it takes physical hits better. It's notable that the extra boost from Brave nature isn't as beneficial as having a Relaxed Nature since you don't run much Attack EVs, or no EVs at all. With Brave nature and no Attack EVs, Donphan has 154 Attack in 50s, and 303 in 100s. (I apologize since I'm new and I'm not sure if 50s/100s are more common), the Attack is increased by 14 and 26 something points respectively. The Defense however, has a 17 point increase with a beneficial nature (172>189) in 50s, and a 33 point increase (339>372) in 100s, which is higher than the Attack. Unless you require to take out something noteworthy even without Attack EVs, I find Relaxed nature superior to Brave nature.
3 or your Pokes are weak to Fighting, and 3 to Fire. This means you'll need to keep Cofagrigus alive for the entire match since it is one of your Trick Room sources and your only notable defense against powerful Fighting-types like Choice Band Terrakion. Donphan risks being 2HKOed by Jolly Choice Band Terrakion's Close Combat even after Leftovers, and is always 2HKOed after Stealth Rock, or in the case of your Brave nature, always 2HKOed. Heracross is always 2HKOed by Close Combat even after the resistance and Max HP, so it isn't a safe switch in either. That being said Choice Band Terrakion has the potental to sweep your team once Cofagrigus has been removed.
Cofagrigus is also unprotected from status, although you have 2 Pokemon that are immune to Toxic, and 2 Pokemon that can (somewhat) effectively switch into Scald. The occasional Scald burn chance means Magnezone and Porygon2 aren't going to enjoy the switch in either, which makes them more easier to kill, which is dangerous if the latter is knocked out. Jellicent could be a suitable fit into your team like someone else had mentioned, although Jellicent is a pain in your side as well, since it is one of the Scald users.
Heracross isn't really the ideal candidate of a Bulky Attacker that functions in Trick Room.It's more of a fast, powerful attacker. In this case, I would recommend Machamp or Hariyama, since they have better bulk, priority and access to Guts as well. Despite the fact that Heracross has access to 2 powerful STAB moves and more resistances, I find that Hariyama and Machamp have better movepools and abilities to abuse than Heracross. Both possess the elemental punches that allow it to deal with more physical walls such as Gliscor, Forretress and Skarmory with Ice Punch and Fire Punch respectively. Bullet Punch and Mach Punch are also vital to remove weakened Pokemon such as Latios and Terrakion, and Focus Sash Abomasnow. Since you noted that this team is cleverly used against weather teams, Hariyama and Machamp and abuse Sunny weather set up by Ninetales as well. The former can take Fire hits better due to Thick Fat, and can incinerate Skarmory with a sun-boosted Fire Punch; Machamp can also run a mixed set with Brave nature to use a 100% accurate Fire Blast with No Guard against Skarmory. Did I mention DynamicPunch with 100% accuracy too?
That's all I have to say for your team. Hope my advice was helpful.
