Using the Redshift Mech as I don't think my reactions are really good enough for the regular mechs, in case it's relevant.
On level 2 I purchased two upgrades from the health sacrifice shop, but the health taken didn't match up with what the shop said. I lost five health on the first purchase (12-5=7), but on the second purchase I should have lost three more health(7-3=4?), but instead I was left with 1 health (7-3=1!).
Additionally, after that, even though I managed to collect quite a lot of health thingammajigs to gain extra health, I never got that extra health. I stayed at one health all the way until I died on level four. How does this work?