## *Counterspell*

If the players are within 60 feet of the BBEG when they enact this plan, the BBEG will want to cast *counterspell*. Since the player characters are readying an action to cast a spell, it should be obvious to any BBEG worth their salt that they are about to enact some nasty combo and that they should stop that.

However, the BBEG only gets one reaction, so they can only counter one spell. When *sickening radiance* is cast, they need to decide whether to counter that spell or wait to counter the next spell. If the players had cast the spells individually, the BBEG could have countered them both. But by casting them simultaneously, they guarantee that at least one will hit the BBEG. It also requires the BBEG to use a spell slot (potentially higher than third level, depending how worried they are about the coming combo). This rewards the players' ingenuity without trivialising the encounter.

## *Dispel Magic*

If the BBEG is hit by this combo, they can cast *dispel magic* on *sickening radiance*. They are still stuck inside a *wall of force*, which is not a good place to be, and they may have taken damage from one round of *sickening radiance* if they failed their Constitution save. The BBEG's escape will be sufficiently delayed that the party might gather into a more advantageous position.

## *Disintegrate*

If the BBEG is high enough level to have *disintegrate*, then they can use it to get rid of the *wall of force*. They can then walk out of the *sickening radiance*, although they'll still have faced at least one round of *sickening radiance* (depending on their speed). Forcing the BBEG to use their *disintegrate* on a *wall of force* and not a player character is a substantial advantage.

## Harm the casters, break their concentration

The BBEG might have some way to harm the characters without attacking them directly. BBEGs regularly have minions (and if your BBEG doesn't have minions, why not?). The BBEG would order their minions to focus fire on the two casters, attempting to break their concentration.

However, you specify solo BBEG. If adding minions is not an option, you can instead consider adding lair actions. Lair actions will function as long as the BBEG is alive and can be used to affect the party even if the BBEG can't reach them personally.

Until such time that concentration is broken, though, the BBEG is trapped, unable to fight directly, and making saves against *sickening radiance*. Depending on circumstances, it might be many rounds before the BBEG can escape. This rewards the party's ingenuity.