reflection (PHB p.260):
Three illusory duplicates of yourself appear in your room. Until the end of the spell, the duplicates move with you, mimicking your actions. It moves the position, making it impossible to track which image is real. You can use your action to discard the illusory duplicates.
Each time a creature chooses you as the target with an attack Roll a W20 for the duration of the spell to see if the attack targets one of your duplicates instead.
If you have three duplicates, you must roll a 6 or higher Change the attack target to a duplicate. If you have two duplicates, you must roll an 8 or higher. With a duplicate, you have to roll an 11 or higher.
The AC of a duplicate equals 10+ your skill modifier. If an attack if a duplicate hits, the duplicate is destroyed. A duplicate can be destroyed only by attack that is true. It Ignore all other damage and effects, The spell ends when all three duplicates are destroyed.
A creature is unaffected by this spell if it can not see if it relies on senses other than seeing, such as blindness, or if it perceives illusions as false, such as perception.
Attacks are just Things that require an attack roll (weapon attacks and spell attacks). See p. 194 of the PHB:
If ever the question arises as to whether something you are doing counts as an attack, the rule is simple: when you make an attack roll, you make an attack.
("Attack" has a certain rule meaning in 5e that does not match the normal English meaning: actions and spells that can be called "Attack" attacks in the ordinary language are not necessarily attacks, as far as the 5e rules are concerned.)
If a spell does not say that the caster is casting a magic attack, then reflection does not interact with it. This is evident from the above full description of the spell: The spell effects only occur when the caster is attacked, and their effects are only to change the target of the attack to one of the duplicates. The only way to determine if a duplicate has been hit is to resolve the attack against the AC of the duplicate. There is no provision for reflection Interaction with spells where the target must (for example) make a save throw.
It could be argued that the first paragraph, especially the sentence It's impossible to track which image is realnotes that reflection makes it impossible to reliably target the caster with each effect. There are other spells that affect the targeting of nonattack spells, and these effects are specifically described:
non-recognition (PHB p.263):
The goal can not be targeted by any fortune telling magic …
Antimagic field (PHB p.213):
Spells and other magical effects, such as: For example, a magical missile or a sorcerer aiming at a creature or an object in the ball will not affect that target.
If reflection We would assume that the description describing the interaction contains a specific clause that affects the targeting of non-attack spells. For example, something that begins with "When a creature targets you with a non-aggression spell …". But there is no such formulation; The effects described are only for attacks.
You could argue that too reflection clearly creates illusions that are valid targets for spells, so an enemy spellcaster inadvertently targets one of those illusions.
However, reflection does not succeed illusions; it created illusory duplicatesand it specifically describes all of their effects. Spells that create illusions (like main or little illusion) have different effects (and do not specify what happens when attacked by a spell, attack or otherwise).
So, to look at the two spells in the question:
thwart (PHB p.219):
Necromantic energy washes over a creature of your choice that you can see within range, removing moisture and vitality. The goal must make a constitutional saving throw,
Magic rocket (PHB p.257):
You create three glowing arrows of magical power. Every arrow meets a creature Your choice, which you can see within easy reach.
Magic rocket only hits the creature that affects her reflectionand does not affect the pictures at all. It is not an attack, as no attack roll is executed. it just hurts. thwart also ignores the images and influences the target, as it is not an attack either.