You've fought a lightbulb, then a robotic lettuce, now you're fighting a six-legged spider. As the final enemy Digimon, Armageddemon is quite tough.I really hope you're not arachnophobic.
Armageddemon hasn't gained any attacks since the last time you fought him. His only attack is powerful but he isn't as fast as Bulbmon. Most Digimon should be alright here if they can survive one or two attacks from him. Don't bother with dark-element attacks, they'll barely scratch him. His evasion rate is fairly high, but not as high as Bulbmon's, thankfully.
It's important to remember that Armageddemon has the highest HP figure in the game. I'd estimate it to be around 6500-7000, closer to 7000. If you have Imperialdramon Paladin Mode, Omega Blade might do a fair amount to him. It's a tough battle, but keep it up and when Armageddemon is out, you win.