Hm, I'm really not a fan of mob griefing. As a similar idea, though, I thought of adding dopey vulture-like birds that fly low above deserts and occasionally drop egg-bombs that pop when they hit the ground.
That's a cool mechanic. Need to do some thinking about the mob itself.
Also cool, but I kind of feel like giving beasts military-like coordination would break their characterization as animals and disjoint the design. Maybe a hostile sentient race rides these beasts into battle?
About the avian bomber, I'm thinking what if it scooped up clumps of sand (passed through the blocks but didnt destroy any) in the dessert with extremely large claws or, to add a more unique look, scoop up sand in their mouth or open a chest cavity.
With the tameable fire turret, I'm thinking it could spawn in the somewhat rare above-ground lava pools at night. it could work as a sort of ambusher creature that has a slightly large back/shoulder that pokes above the lava as it croutches in wait. It would then leap into the air and slam down onto the ground by the player and attack with an abundance of fire-related attacks that could include;
-breathing out a short range stream of fire and spinning in a circle
-pausing to lob multiple splash damage fireballs around the player
-smacking with a large bony tail
-lighting itself on fire and charging at the player
-creating a sort of growling expression and spitting fire through its teeth that spreads in 3-5 directions and reaches up to 4 blocks away
It could be tamed via doucing it in water when it lights itself ablaze. that could leave it stunned (literally or just shoked) and gives you time to attempt to tame it the same way you'd tame a horse till it knocks you off and sets itself ablaze again.
Now concerning the fire beast that uses a military stratgey, this could be changed into technologically advanced goblins that could rome the land paving a path for their empire
They could be tamed by a means currently unknown and be used to stage battles with barakoa
The goblins would focuse on small task forces with 2 fire starters (have the miniture mobile mortars) and 3 shield units (will stay in close proximity to the fire starters and will knock you back with their shields, maybe also perriodically push down thier shields to use a crosebow thats mounted on its inside)
The goblins would spawn again near villages and could add a theme to your mod that shows an evil force attempting to convert a magical word into machine