Alright, a few that I missed
Kaalia of the VastAnd then some general dragons that I'm filling out that "15-20 dragons" with:
Hoarding Dragon
Skithiryx, the Blight Dragon
Spellbound Dragon
Destructor Dragon
Flameblast Dragon
Forgestoker Dragon
Hoard-Smelter Dragon
Mana-Charged Dragon
Mordant Dragon
Balefire Dragon
Dragon Mage
Knollspine Dragon
Furnace Dragon
Slumbering Dragon
Dragonlord Ojutai
Harbinger of the Hunt
Icefall Regent
Sunscorch Regent
Thundermaw Hellkite
Dragonlord Dromoka
Dragonlord Kolaghan
Dragonlord Silumgar
Dromar, the Banisher
Hellkite Charger
Hellkite Tyrant
Intet, the Dreamer
Keiga, the Tide Star
Kokusho, the Evening Star
Malfegor
Niv-Mizzet, Dracogenius
Niv-Mizzet, the Firemind
Prossh, Skyraider of Kher
Rith, the Awakener
Savage Ventmaw
Scourge of the Throne
Steel Hellkite
Teneb, the Harvester
Yosei, the Morning Star
Deathbringer Regent
Dragonlord Atarka
Siege Dragon
Tyrant's Familiar
Bogardan Hellkite
Nicol Bolas
Scourge of Kher Ridges
How many is that? 45? Hmmm...ok, going to have to break this down.
Two things that strike me:
1. priority goes to those that provide card advantage, or removal.
2. Additional priority goes to those that don't require mana to do so.
Hoarding Dragon -- maybe (+1 card, an artifact. I have specifically
Amulet of Vigor in mind, but even that might not be all that wonderful by the time I play a 5 mana dragon and it dies.)
Skithiryx, the Blight Dragon -- no
Spellbound Dragon -- maybe (looting is semi card advantage)
Destructor Dragon -- no ish (it's a 2-for-1, but not great)
Flameblast Dragon -- maybe (repeated killing...but only for a mana sink)
Forgestoker Dragon -- no (repeated killing, but underwhelming at it for mana)
Hoard-Smelter Dragon -- maybe (repeated artifact kill...but costs mana)
Mana-Charged Dragon -- maybe (fails my criteria, but it's hillarious)
Mordant Dragon -- tentative yes (kills things without mana)
Balefire Dragon -- yes (much stronger Mordant Dragon)
Dragon Mage -- maybe (draw 7 is pretty good, I just fear other decks can take advantage of it better)
Knollspine Dragon -- yes (card draw, plenty of it)
Furnace Dragon -- yes (mass artifact exiling)
Slumbering Dragon -- ...maybe (it's just big, but the fact that it costs 1 is relevant; I'll get to that later)
Dragonlord Ojutai -- yes (card draw)
Harbinger of the Hunt -- maybe (sweeper, but costs mana)
Icefall Regent -- yes (removal; can shut down certain problem commanders)
Sunscorch Regent -- yes (it is "just big" but in a way that's very good in EDH, and lifegain will probably be relevant)
Thundermaw Hellkite -- yes (it's not much AoE, but it's free, and it's a tap, and it's haste)
Dragonlord Dromoka -- yes (I own it; lifegain may be relevant)
Dragonlord Kolaghan -- maybe (it's another source of "your creatures have haste"--actually it belongs more in the "buffing" category)
Dragonlord Silumgar -- yes (removal)
Dromar, the Banisher -- maybe (it's...powerful, but costs mana, but it also hits my stuff...)
Hellkite Charger -- maybe (that's a lot of mana, but a second attack step is good)
Hellkite Tyrant -- yes (steal all the artifacts)
Intet, the Dreamer -- yes (the ability costs mana, but it nulls the mana of the card, so it's a win. And card draw)
Keiga, the Tide Star -- yes (removal)
Kokusho, the Evening Star -- yes (lifegain)
Malfegor -- yes, I think (removal, and just hits a different vector than the damage based removal that most dragons do)
Niv-Mizzet, Dracogenius -- yes (card draw)
Niv-Mizzet, the Firemind -- yes (card draw)
Prossh, Skyraider of Kher -- no (a little bit tempting just for the "sacrifice a creature:" text but...no)
Rith, the Awakener -- no (powerful card but...I won't be running ways to make saprolings good)
Savage Ventmaw -- yes (a bit unorthodox, but yes, 6 mana is cool)
Scourge of the Throne -- yes (completely free extra attack? ok)
Steel Hellkite -- yes (costs mana, but it kills literally anything if you're using it)
Teneb, the Harvester -- yes ("from a graveyard" you say?)
Yosei, the Morning Star -- maybe (yosei is disgusting with recursion; don't have much; but locking down one player for one turn is...a bit borderline?)
Deathbringer Regent -- yes (it's a wrath that will basically always be active)
Dragonlord Atarka -- yes
Siege Dragon -- yes (note that it doesn't have to get through unblocked)
Tyrant's Familiar -- yes (note that it doesn't have to get through unblocked)
Bogardan Hellkite -- y...maybe (the comparison to Atarka isn't looking great here)
Nicol Bolas -- yes? (I suppose technically this should be a maybe if I was being consistent, but fuck it, it's nicol bolas)
Scourge of Kher Ridges -- maybe (costs mana, etc)
ok...next pass...taking Spellbound Dragon over Mordant Dragon, but mostly looking at the yes count...this is still 26
Spellbound Dragon -- maybe (looting is semi card advantage)
Balefire Dragon -- yes (much stronger Mordant Dragon)
Knollspine Dragon -- yes (card draw, plenty of it)
Furnace Dragon -- yes (mass artifact exiling)
Dragonlord Ojutai -- yes (card draw)
Icefall Regent -- yes (removal; can shut down certain problem commanders)
Sunscorch Regent -- yes (it is "just big" but in a way that's very good in EDH, and lifegain will probably be relevant)
Thundermaw Hellkite -- yes (it's not much AoE, but it AoEs for free, and it's a tap on all blockers, and it's haste)
Dragonlord Dromoka -- yes (I own it; lifegain may be relevant)
Dragonlord Silumgar -- yes (removal)
Hellkite Tyrant -- yes (steal all the artifacts)
Intet, the Dreamer -- yes (the ability costs mana, but it nulls the mana of the card, so it's a win. And card draw)
Keiga, the Tide Star -- yes (removal)
Kokusho, the Evening Star -- yes (lifegain)
Malfegor -- yes, I think (removal, and just hits a different vector than the damage based removal that most dragons do)
Niv-Mizzet, Dracogenius -- yes (card draw)
Niv-Mizzet, the Firemind -- yes (card draw)
Savage Ventmaw -- yes (a bit unorthodox, but yes, 6 mana is cool)
Scourge of the Throne -- yes (completely free extra attack? ok)
Steel Hellkite -- yes (costs mana, but it kills literally anything if you're using it)
Teneb, the Harvester -- yes ("from a graveyard" you say?)
Deathbringer Regent -- yes (it's a wrath that will basically always be active)
Dragonlord Atarka -- yes
Siege Dragon -- yes (note that it doesn't have to get through unblocked)
Tyrant's Familiar -- yes (note that it doesn't have to get through unblocked)
Nicol Bolas -- yes? (I suppose technically this should be a maybe if I was being consistent, but fuck it, it's nicol bolas)
Need to cut at least six more. Anything I'm hesitating on is probably out, soo...Nicol Bolas, Spellbound Dragon. I don't think I want to cut much that costs 4-5, cause you know, curve matters. I think I want to cut one Niv Mizzet because the mana cost kinda sucks, and it would be unfortunate to have two in my hand. Hmm...I dunno which is better in this deck. Dracogenius is cheaper, though, so cut Niv-Mizzet the firemind. Umm...I have three cards on lifegain; if I'm keeping the 5 drops, and running Dromoka because I own it, that means cutting Kokusho. Siege Dragon...ehh...I have lots of ways to clear small creatures, and 2 damage won't always do things. Knollspine Dragon...you know, this is a little bit winmore, even by EDH standards; if I have dragons in play and attacking and not being blocked, I can refill my hand, yes. But then there'll be times when I can't attack, and just want to play a dude. OK, this reduces us to...
Balefire Dragon -- yes (much stronger Mordant Dragon)
Furnace Dragon -- yes (mass artifact exiling)
Dragonlord Ojutai -- yes (card draw)
Icefall Regent -- yes (removal; can shut down certain problem commanders)
Sunscorch Regent -- yes (it is "just big" but in a way that's very good in EDH, and lifegain will probably be relevant)
Thundermaw Hellkite -- yes (it's not much AoE, but it's free, and it's a tap, and it's haste)
Dragonlord Dromoka -- yes (I own it; lifegain may be relevant)
Dragonlord Silumgar -- yes (removal)
Hellkite Tyrant -- yes (steal all the artifacts)
Intet, the Dreamer -- yes (the ability costs mana, but it nulls the mana of the card, so it's a win. And card draw)
Keiga, the Tide Star -- yes (removal)
Malfegor -- yes, I think (removal, and just hits a different vector than the damage based removal that most dragons do)
Niv-Mizzet, Dracogenius -- yes (card draw)
Savage Ventmaw -- yes (a bit unorthodox, but yes, 6 mana is cool)
Scourge of the Throne -- yes (completely free extra attack? ok)
Steel Hellkite -- yes (costs mana, but it kills literally anything if you're using it)
Teneb, the Harvester -- yes ("from a graveyard" you say?)
Deathbringer Regent -- yes (it's a wrath that will basically always be active)
Dragonlord Atarka -- yes
Tyrant's Familiar -- yes (note that it doesn't have to get through unblocked)
Mmm...I'm not feeling great about cutting Kokusho. On the other hand, this is a casual EDH deck I don't plan to spend a ton of money on, and he costs money. Could swap Thundermaw Hellkite (being another money card) but...naaah, the haste is super relevant with the triggers; getting through unblocked is super relevant with the triggers; whatever, this set of 20 is fine.