From publisher blurb:
The Multiclasser's Manual is just what it sounds like; a collection of resources for building compelling multiclass character in Level Up: Advanced 5e. However it also isn't just that. In this volume you will find:
13 archetypes, including 4 brand-new ones
Synergy feat chains for 27 two-class combinations (24 of which are brand-new) and one for a three-classcombination.
Cleric/Fighter
Cleric/Rogue
Cleric/Wizard
Fighter/Rogue
Fighter/Wizard
Rogue/Wizard
Adept/Cleric
Adept/Sorcerer
Artificer/Druid
Bard/Ranger
Bard/Warlock
Berserker/Ranger
Cleric/Herald
Cleric/Marshal
Druid/Warlock
Elementalist/Sorcerer
Esper/Warlock
Fighter/Herald
Herald/Wielder
Marshal/Ranger
Marshal/Rogue
Ranger/Rogue
Ranger/Witch
Ranger/Wizard
Savant/Scholar
Sorcerer/Wizard
Warlock/Wielder
Cleric/Fighter/Herald
17 "profession feats" allowing some "soft multiclassing" by learning a couple of "knacks" from the associated class.
4 combat traditions
18 spells
1 magic item
This releases covers all 13 classes in the A5E core rules, along with the artificer, savant, esper, elementalist, wielder, scholar, and witch classes from supplemental material and the third-party community.
Whether you're building a multiclass character covered by one of the combinations or a single-classed character that wants to swipe a few features from another class, this has you covered!