Wardens cannot be killed, only slowed down

Its established that the warden isn't something the player should be aiming to kill. If the warden can take damage it will be killed with cheese strategies. Instead of damage reducing the warden's hp and eventually killing it, what if damaging the warden drained its vitality, slowing it down and potentially applying weakness. Players have ways to interact with the warden directly in a way that increases their odds of survival but never actually killing it.

Vitality continuously regenerates. Give a way for the movement speed to scale with vitality, while still having a minimum value.

warden speed = base speed*(0.15+(current hp/max hp))

To prevent spam of a single damage type, use a system similar to move staleing from smash. Repeated damage from the same source has diminishing returns. The first 10 ticks of damage from being in lava deal 4 damage, but over time this reduces to a trivial amount until it is below the base vitality regen rate. A temporary slow. The goal here is to encourage tactical diversity and prevent continuous damage sources like lava and wither stun locking the warden. A player using many damage types sources, fighting creatively can keep the warden slowed for a while before vitality regen overcomes dps. Some time after dropping aggro, the damage reduction/staleling is reset. 

I'm aiming for a T-1000 terminator vibe here, you can slow it down enough to escape, but nothing you can carry will ever be enough to kill it, and you are never safe with one around.