I propose that new bombs that resemble tortodrones* and have unique mechanics be made.
How would it work? Well, upon planting the 5* version of the bomb, 5 spots that form a pentagon shape appear around the player.
You would then have to wait for the bomb's explosion, which is 5 tortodrone gun bullets forming a temporary inpenetratable wall** around you that would keep enemies away and give the player time to prepare the charge attack of a stronger weapon, for example, a calibur/nitronome charge could work very well.
Also, the shape and the number of spots that appear around the player change when the player upgrades the bomb, aka 3* - 3 spots and triangle shape, 4* - 4 spots and square shape, 5* - 5 spots and pentagon shape.

Now, for the bomb's alchemy line:

Normal dmg:
2* Shard Bomb -> 3* Shell Cracker -> 4* Shell Buster -> 5* Tortoboom
Piercing dmg:
2* Splinter Bomb -> 3* Shell Clawer -> 4* Shell Biter -> 5* Tortohowl
Shadow dmg:
2* Dark Matter Bomb -> 3* Shell Breather -> 4* Shell Swiper -> 5* Tortograve
Elemental dmg:
2* Crystal Bomb -> 3* Shell Tickler -> 4* Shell Shocker -> 5* Tortocrash
(the names suck btw, feel free to suggest your own ideas)

*Tortohowl
**the wall only is inpenetratable at 5*, other versions of the bomb have gaps that let enemies through