This came up last night in our D&D session.
Situation: A wizard cast Evard's Black Tentacles; another creature fails its Dexterity save and is restrained by the tentacles. This spell requires concentration.
While maintaining concentration, the wizard casts Wall of Fire on a good chunk of enemies. This spell also requires concentration.
Are the enemies still "restrained" by Evard's Black Tentacles when the Wall of Fire is initially cast, and do they have disadvantage on Dexterity saving throws against the Wall of Fire? Or does casting the spell immediately end the Evard's Black Tentacles spell, giving the creatures enough time that they are not restrained and thus they do not roll the Dexterity save at disadvantage?
Both of these spells require concentration so they cannot both be active at the same time.