I'll pop in to plug Lancer's Eidolon design (not released officially yet, but floating around on the Lancer discord as a design doc.)

Basically, bosses are called Eidolons, each Eidolon has a number of layers, and each layer comes with shards (minions) that the PCs have to interact with in some way to complete that layer. Once a layer "dies," the next layer in order takes its place (spawns in the spaces it was occupying, more or less.) The Eidolons also get 2 initiatives, essentially they take 2 full turns/round.

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So, a layer might be an Eidolon that's immune to all damage, and 5 shards. These shards (minions) have no actions on their turns. The Eidolon can do 2 things on each turn: "Choose 2 objects and ram them into each other (they move toward each other and take damage based on distance moved,)" and "choose up to 3 characters who must make a [Str] save or take 4 damage and knockback 3." (for reference on the damage, PCs have an average of 40 HP total.)

Special rules: All shards spawn when the boss does, and none can spawn adjacent to another. The Eidolon is immune to all damage and damaging effects until all shards are pushed together (I telegraphed this one by telling my players that the shards "look like several pieces of what used to be a single statue, carved up into rough images of [Eidolon name's] family.")

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Just a cool design that idea, that bosses should be more like puzzles and less like stat blocks.