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Looking at these units, it seems that 50 HP might be too little for them – it turns out to be roughly the same as liches. These trolls are so bulky that it looks like they should be able to tank and withstand attacks. Although their attack, defense, and damage are high for a Tier 5 unit.
Just my opinion – around 70 for the non-upgraded version and 80-90 for the upgraded/elite version would be ideal, with a slight reduction in attack, defense, and damage.