there should be special units with 1hp (as a unit not a cymanti trait) that will explode when desired, having no fighting capabilities and maybe has a version that can go further higher on the skill tree or another one higher on the skill tree that might have a larger explosion or a stronger explosion.
there could even be special parameters like a special building that can only be built once like the ice bank that allows someone to upgrade their explosive minion, not like the skill tree because this one would be sort of like a stage where you might be able to sacrifice a unit or an amount of health over time to create different variations of exploders.
eg a exploder that once exploded can take over units costing either 3 shamans or 40 hp. or a exploder that might give a poison/freezing effect or a exploder that might deal damage but also summons a monster like the rabbit.
like wise with something this unique it could perhaps take a conduit each from 4-8 settlements with the centre settlement having the alter to advance the exploders.
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