Draconic Lore
Instant
This spell costs 
less to cast if you control a Dragon.
Draw three cards.
The wyrmling studied the ancient carvings and dreamed of a day when her own exploits would be immortalized in stone.
Tom Babbey
Rulings
The cost of Draconic Lore is determined and locked in as you cast it before any mana abilities are activated and before any player can respond. Notably, this means that no player can respond to remove your Dragon before the cost is reduced, and if you sacrifice that Dragon as part of a mana ability, the cost won't be increased.
(wotc • 2022-06-10)
Rulings
The cost of Draconic Lore is determined and locked in as you cast it before any mana abilities are activated and before any player can respond. Notably, this means that no player can respond to remove your Dragon before the cost is reduced, and if you sacrifice that Dragon as part of a mana ability, the cost won't be increased.
(wotc • 2022-06-10)