What if I moved dash to space then used shift as the alchemy key? You'd hold shift, use QWEASD to mix your stuff, then let go of shift to return to normal controls.I expect those keys to be rebindable, so anyone could swap them.
It could result in some frustrating experiences where you forget to turn off the alchemy mode and try to fight an enemy, only for you to not movejust make it a modifier key you need to hold to stay in alchemy instead of a toggle. I think having alchemy mixing work only when you hold the key would be easier not to accidentally leave it on.
when alchemy is turned off, you could still use Q and E key for things like weapon switching and clearing chemicals.
Basically I propose you to implement your controls as two states that change depending on if you hold down the space/shift.
for example:
None Mixing state (without holding Shift)
Q - use chemicals on yourself
E - clear chemicals
WASD - movement
SPACE - Dash with movement direction
Mixing State (While holding Shift)
QWEASD - all chemicals
SPACE - Dash towards the cursor
Both states
LMB - Primary Attack
RMB - Secondary Attack
Scroll Wheel - weapon switch