Lazy Capcom. This is just the first of 4 repeated bosses Dante’s gonna face:

Human / Devil Hunter modes

1. Basically, if Echidna reveals herself and floats around casually, jump and either spam Aerial Rave with Rebellion or Full House (Killer Bee) rebounds (requires the ability Enemy Step) with Gilgamesh.
    
2. When she transforms into the seed-laying form, you can try to Air Hike up towards Echidna’s main body to attack (if you can), or you can just spam Aerial Rave + Shotgun on her belly. The Chimera Seeds she lays don’t really give you any trouble so you can ignore them as always.
    
   
3. When she transform into a dragon, you can spam mid-air Shotgun shots and side roll or Dash/Sky Star with Trickster away when she charges at you.
    
   
4. When she lies on the ground with her tail under the ground, unleash DT and abuse these:
   1) If this is your first play-through: DT + Rebellion’s ground combos.
   2) If this is a replay: DT + Real Impact or spam Pin Up (Lucifer), etc
    
   That alone will easily take out a huge chunk of her life. Don’t worry about getting knocked back by her tails; your DT should be able to prevent that for at least a while. And if you do get knocked away, just Stinger or Full House your way back to her and repeat the whole process until, hopefully, she gets dizzy. Then repeat it all again anyway. o_o

Sons of Sparda / Dante Must Die modes

Now that you've got all of Dante's weapons, it's time we play the game a little more stylishly =P This time, I'll be utilizing Pandora's Box, just cause it's fun and cool and it kicks ass.

1. Assuming that you have zero disaster gauge to begin with, once the battle, run as far towards the screen as you can get and quickly do Pandora's Revenge (mega-laser attack) to refill a good bit. Echidna will swing her tail around in that time but it won't hit you from that far.
   
   Note: In DMD, right after the above step Echidna will go into the form where she sits on the ground. And if she does that you can stay where you are and perform just one more Revenge. Her initial tails will not get you from that far.
    
2. Echidna will then fly away and start going into one of her few forms. If she turns into dragon form:
   
   You can carefully fire Pandora in mid-air a few times while waiting for Echidna to charge at you. Once you see her coming at you, prepare to shoot on ground with Pandora (Epidemic) at the dragon's head. It'll require some timing as Pandora isn't exactly the fastest gun and you'll have to shoot earlier than usual to counter the dragon. If it hits, your style rank will increase by 2~3 grades instantly. (e.g. from D to B) This is entirely optional though if you wish to play safe, where you'll probably by Sky Star'ing all over the place to avoid her charge attacks.
    
3. If she reveals herself while floating around:
   Run/Air Trick/Sky Star (Trickster) over to her and start spamming any aerial combos. An easy style-racking one would be to do both Rebellion and Yamato's Aerial Rave by switching from Swordmaster to Darkslayer after each move.
   
   If you see her about do her hair swing attack, quickly switch to Trickster and Sky Star away before Air Trick'ing back to her to continue the rampage. Shoot Pandora in mid-air from time to time whenever you can to fill up your disaster gauge.
    
4. If she sits on the ground:
   Check and see if you have enough DT and disaster gauge. If you do, switch to Gunslinger, DT, triple-jump (Dante can triple jump when DT'ed) and do Pandora's Argument (missile factory). If you have enough disaster gauge to perform two Arguments at once, Echidna will change forms immediately, which is good cause her split tail attacks are helluvannoying!
    
   If you don't have enough of either DT or disaster gauge, stay in Trickster mode and keep shooting Pandora in mid-air whenever you can during safe openings (after the split tails have emerged from the ground) while dashing/Sky Star'ing away whenever in danger. Approach Echidna herself for close combat only if you think you're safe enough as the tails could still hit you from anywhere while you're busy slashing.
    
5. If she goes into her seed-laying form:
   Jump/Air Trick towards her egg-laying belly and spam Rebellion's Aerial Rave + Pandora's mid-air shots and ground shots. Rotating between these 3 moves rack up a lot of style points for some reason.
    
   The Chimera Seeds attack sometimes but you could get hit by Echidna while in the middle of it as well so it's really up to you to decide whether it's better to kill or just ignore them. They may screw up your lock-on on Echidna when you want to lock on her though.

Video demo on DMD | Mirror link on Youtube [9.02 mb]