My suggestion is simple: to change the appearance of mob spawners to fit the creature.
Instead of the cube form now, it would be an egg cluster for spiders, a tombstone for zombies, and a bone pile for skeletons.
In spider dungeons,whenever a spider spawns, it shows a small spider crawling up through
the cluster, then growing to full size and becoming hostile. For zombie dungeons, the zombies would spawn when a zombie breaks through the ground fist first. Skeletons would rise from a heap of bones, the bones flying up to form a skeleton, head down.
Mob spawner change