We've seen some examples of this, during last anniversary and most recently with the large grave scarabs tied to zombies.

I think that they could really make for interesting and difficult content, especially if they were to tie easier enemies to bulkier or more difficult ones, making for faster or slower solutions depending on your team's overall strategy.

Imagine a special giant lichen colony resembling a glop drop that spawns glop drops and when killed, becomes n-1 smaller lichens where n is the number of smaller lichens it was created from. These smallest lichens could then turn into 2-3 glop drops each when killed. The amount of coordination required to take down such a beast would be phenominal under all but the simplest circumstances.

Similarly, we could forseeably get enemies that incorporate turrets into this- if you kill that scuttle bot, it drops down, sizzles, and grows into a gun puppy resembling a scuttle bot.

Devilites that summon trojans when killed?

Grievers that become silkwings?

Gremlin demos that become grievers?

I honestly wondered whether to put this in general discussions or here, because I think that the developers would be foolish to ignore these possibilities.