The New TFT Traits in Set 7.5 Explained
The official description from Riot Games about Lagoon is:
"Lagoon units gain bonus Ability Power and Attack Speed. A Seastone appears on the board that grants loot as Lagoon units cast Abilities over time."
Lagoon is, on paper, the more tame of the two new traits in Set 7.5. It grants bonus AP and attack speed, which is sure to combo well with Mage units that want to cast as often as possible for as much damage as possible. What makes Lagoon interesting is that the more your Lagoon units cast, the more rewards you get over time. This makes Lagoon work similar to previous traits like Mercenaries, where even if the trait itself isn't the strongest, you're encouraged to play the units as long as possible so you can reap the plentiful rewards.
The official description from Riot Games about Darkflight is:
"The unit in the Darkflight hex is sacrificed at start of combat, granting a copy of a random item they have to each Darkflight champion, and bonus health to each."
Darkflight is replacing the Legend trait present in Set 7: Dragonlands but with a twist. Rather than merely giving one Legend champion all of a sacrificed units' stats, a Darkflight sacrifice keeps it simple and instead grants all Darkflight champions bonus health and an item. This adds a new layer of strategy since you have to be very careful about which items you want all your Darkflight champions to receive. Make sure you only place on item on a unit to be sacrificed, though, or it will randomly pick one to be distributed for you.