I'm guessing that, at first, most people do exactly what I did when building a Tiamat deck: just shove all the best dragons you have together. But as I played, I kept finding that most of my dragons didn't do much.

I realized that the only dragons I ever wanted to see before Tiamat were Fearsome Whelp, Scaled Nurturer, Atsushi, the Blazing Sky, and Terror of the Peaks while the only dragons I ever wanted to fetch with Tiamat were Terror of the Peaks again, Wrathful Red Dragon, Earthquake Dragon, and a wild card slot that depended on what the opponent was doing: Atsushi if I expected them to kill whatever I played, Inferno of the Star Mounts if I expected them to counter whatever I played, and Old Gnawbone if I expected neither.

Since all eight dragons I kept playing were red or green, I cut almost all white, blue, and black from the deck and went all in on two things: ramp to get to Tiamat and the important dragons as quickly as possible, and burn that can either keep me alive or close out the game. Nothing else matters.

I don't even really want to play Rith, Liberated Primeval or Miirym, Sentinel Wyrm--and I almost never do! That said, I don't like 4-mana ramp spells enough to cut them for Migration Path and Vastwood Surge, there are only so many great burn spells, and I don't have enough lands to feel like Explore, Growth Spiral, or Joint Exploration belong here. Rith and Miirym do at least combo well with Terror of the Peaks, creating a backup plan if the opponent kills Tiamat to preemptively stop Earthquake Dragon from coming into play.

Lozhan, Dragons' Legacy might seem like a strange omission since this is basically a Terror of the Peaks deck and Lozhan is very similar--and even better in one way since killing Lozhan in response to a cast trigger won't stop the damage. Still, the gap between a 5/4 and a 4/2 is gigantic. It's about surviving Lightning Bolt vs. dying to Shock and Stomp. It's about Meathook Massacre costing 6 instead of 4. It's about the fact that Llanowar Elves can kill Lozhan with Blizzard Brawl and Ascendant Packleader with no counters can kill Lozhan with Ram Through, Bite Down, or Master's Rebuke. Bottom line, I can play Terror of the Peaks early and there's a chance it survives, but Lozhan never will.