Dragalia Life #6 has Ranzal checking the temperature of the spring before getting in. It makes sense since he's a Wind unit that's weak to Fire attacks.
One of Fjorm's abilities obtained from the mana circle is Skill Prep 100%. In her home game, Fire Emblem Heroes, she comes with the skill Shield Pulse, which reduces the skill cooldown by 2 at level 3 if the unit has a defensive skill like Pavise and if it's the first turn. Her Secret Art, Ice Mirror, qualifies as such, and with its cooldown of 2, Fjorm has it ready from the start.
The reason why Marth is such a Game-Breaker against High Midgardsormr is because by the end of his own game, he will have racked up several dozen manakete kills. A dragon like regular or High Midgardsormr would be no issue.
Alfonse can obtain Curse Resist 100% from the Mana Circle. In his home game, he is cursed by Hel, Queen of the Underworld, that he will die in 9 days, the same curse that killed his father Gustav. He boasted to Hel that he'll use that time to find a way to kill her.
"The Hunt for Harmony" shows that Luca and Sylas, in their youth, have basically invented mustard gas. In small bombs, they're good for stink bomb pranks, but in industrial quantities if the Empire got their hands on that recipe along with refinement, it would be a very catastrophic to the point of using it very straight like World War 1!
The flavor text for the 5 star tier 3 shadow lance weapon, Mistilteinn, describes it as not the name of a single weapon, but also having different forms like a sword, a lance and a plant sprout. An evil weapon that changes form? Are we talking about Soul Edge?