Ultimate Dragons adds abilities to dragons.
Dragon Combat Overhaul comprehensively changes dragon combat behaviors.
I like DCO as it has less of a script load than Deadly Dragons. Though they are compatible.
Reading the descriptions it looks like DD boosts the health and fire power of the dragons while DCO changes how they fight. //I had issues running Deadly Dragons on my build. DCO works beautifully and some of the things it adds are pretty damn amazing. DCO improves the dragons a larger selection of attacks and (this is the kicker) gives them mass. When a dragon lands next to you, if you don't block you can easily get knocked off your feet. If you get DCO, make sure you get "D13 Faster GET UP STAND UP animation vanilla friendly" by DarkAngel13 https://www.nexusmods.com/skyrim/mods/17491/  as well, otherwise you're going to be spending a lot of time watching your character flail on the ground. One of the biggest things in DCO I have noticed is that dragons use more shouts and more powerful shouts. Dragons can summon blizzard, meteors and more dragons with shouts. Hearing a shout and seeing sky clear for a moment before blizzard rains on you.
https://www.reddit.com/r/skyrimmods/comments/1yqnxw/deadly_dragons_or_dragon_combat_overhaul/
https://www.reddit.com/r/skyrimmods/comments/2oshgf/dragon_combat_overhauls_mod_page_is_offputting/
    Dragon Combat Overhaul - hardcore, you will die sometimes
    Deadly Dragons - midrange difficulty at default settings, but very customizable to make easier or
crazy hard. This is the one I ended up using. (some issues reported -NB)
    Ultimate Dragons - more about making dragon attacks more varied and interesting than more
difficult.
"I just want to point out that all three are compatible, it's not an either or."
DCO is worth it. Protip that 99% of people don't seem to know. Blocking (or using Magic Wards) blocks the knockdown effect entirely. Don't want to ragdoll everywhere using DCO as a melee character? Don't stand there mindlessly attack and/or doing nothing and drooling while the Dragon does what he wants to you. Its my favorite dragon combat mod. It makes the dragons feel so much bigger and scarier, especially when they do the dive bombing thing. The dragons are much more formidable when whey can knock you on your ass with their wings, or body slam you from the sky. (Can disable Knockdown attack in DCO's MCM settings.) Its my favorite dragon combat mod. It makes the dragons feel so much bigger and scarier, especially when they do the dive bombing thing. The dragons are much more formidable when whey can knock you on your ass with their wings, or body slam you from the sky.
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