By and large, Dragons are made for damage, not denials, so this one is a fairly short list!
As always, I like to first break down the monsters by speed:
- General Darmith
- Drekk; Greedy Dragon; Learnean
- Blockheart; Darmith's Pet; Goran; Killeraptor; Yndra
- Eggeater; Megaosteum
- M-2 WYVERN
No surprise here, Frostwrath is a great denier. With the fastest speed among Dragons, he is without question designed to deny. His skills focus on freezing and draining energy. He's got 3 freeze skills (one of which is a must-have AoE freeze) and 3 skills that apply stamina leak (one them drains stamina on top of applying the leak). Lastly, another skill drains 50% stamina from a single target. His Energized trait is probably the worst trait in the game, but his skills and stats are great.
When in magic wars, you'll often face Eggeater and for good reason. Firstly, he can possess the whole enemy team (possession, in my opinion is way better than any stun or freeze: not only will you not get attacked, but the enemy attacks itself). His Multi Effect Eggs skill burns and blinds the whole enemy team (blind: the OG deny skill). His other attacks just do a great job of dealing out damage (poison and nightmares). Like many possessors, he's immune to possession himself.
These monsters I don't necessarily recommend using as deniers, but for comparison purposes here, I mention them. Tier 2:
Learnean is a monster designed with the purpose of burning, poisoning, and dealing some other effects. Among those other effects are stunning single enemies (on 2 different skills), applying stamina leak, and draining half a monster's energy. He's also Hardened, which isn't bad.
I only mention M-2 WYVERN here because of two skills. One drains 50% stamina from the whole enemy team, the other stuns a single enemy. In my opinion, he's more of a secondary attacker (he burns enemies and can deal 80 special damage to a single target).
Trilops is immune to stun and has THREE skills that stun single targets. It's very unlikely that you'll use Trilops as a denier, but the skills are there.
Megaosteum, General Darmith, Greedy Dragon, Dracontium, Darmith's Pet, Killeraptor, and Yndra are undisputed attackers.
Tryon and Blockheart are more attack-based (although they're not the best in my opinion). Goran is a tank and Drekk is a healer.