Third-level spells are crucial for wizards in D&D ... editions of D&D have been changed so they only target one being in 5e. Haste is a good example of this. Slow was thankfully not changed ...

When you and your partner both cast this spell using spell slots of 4th-level or higher, for each spell level above 3rd, all creatures who gained advantage on a d20 test also gain a +1 to the roll. If ...