Activate Scion of the Ur-Dragon by paying {2}.
Holding priority, activate Scion of the Ur-Dragon a second time by paying {2}.
Resolve the first Scion of the Ur-Dragon ability, searching your library for Moltensteel Dragon, putting it into your graveyard, causing Scion of the Ur-Dragon to become a copy of Moltensteel Dragon until end of turn, and shuffling your library.
Activate Scion of the Ur-Dragon by paying {R/P}, giving itself +1/+0 until end of turn.
Repeat step 4 five additional times.
Resolve the Scion of the Ur-Dragon ability from step 1, searching your library for Skithiryx, putting it into your graveyard, causing Scion of the Ur-Dragon to become a copy of Skithiryx until end of turn, and shuffling your library.
If Scion of the Ur-Dragon has summoning sickness, activate it by paying {B}, giving it haste until end of turn.
Deal combat damage with Scion of the Ur-Dragon, causing an opponent to get ten poison counters and lose the game due to lethal infect damage.

Target opponent loses the game

Scion of the Ur-Dragon

Skithiryx, the Blight Dragon

Moltensteel Dragon

Cast Skithiryx by paying {3}{B}{B}.
Skithiryx enters the battlefield, triggering Warstorm Surge, giving an opponent at least seven poison counters.
Cast Rite of Replication with kicker by paying {7}{U}{U}, creating five token copies of Skithiryx.
Put all five Skithiryx tokens into your graveyard due to the legend rule.
Warstorm Surge triggers for each Skithiryx token.
Resolve the first Skithiryx trigger, giving an opponent at least seven poison counters.
If the opponent has ten or more poison counters, they lose the game as a state-based action.
Repeat from step 6 for each remaining trigger.

Each opponent loses the game

Warstorm Surge

Coat of Arms

Rite of Replication

Cast Skithiryx by paying {3}{B}{B}.
Skithiryx enters the battlefield, triggering Warstorm Surge, giving an opponent seven poison counters.
Cast Rite of Replication with kicker by paying {7}{U}{U}, creating five token copies of Skithiryx.
Put all five Skithiryx tokens into your graveyard due to the legend rule.
Warstorm Surge triggers for each Skithiryx token.
Resolve the first Skithiryx trigger, giving an opponent seven poison counters.
If the opponent has ten or more poison counters, they lose the game as a state-based action.
Repeat from step 6 for each remaining trigger.

Combos with "Skithiryx, the Blight Dragon"