I, too, enjoy getting all the lichens together into one massive colony. It's hard because sometimes, the smaller lichens merge with each other instead of the larger colony, and if they merge into the orange colony, they can't merge with the big red one anymore.

I also like the second Snarbolax level, where the path splits in opposite ways and you could either go left and fight zombies around tough blocks or go right and traverse a maze of non-destructible blocks linked by a ghost block. I enjoy going down the right path, freeing all the monsters from their cages (for maximum crowns and heat) while still keeping enough blocks connected so that the one ghost block destroys all of them.

In the FSC levels, if I'm allowed to, I like to try and put out all the shadow fires, ostensibly so that they pose no risk to newcomers (but really to satisfy my perfectionist bent).

Destroy everything destructible!

Max level all gear that I won't/can't get rid of, like Proto gear. All else can stay at level 1 for all I care. Darn Radiant drought.