The first issue that comes to mind is the method by which Endurance is calculated - on a log graph that quickly tapers off past a 4 or 5 million level tattoo adding worthless PR.

My first thought was to implement a new equation for calculating Endurance as follow:

y=((x/LargestTattoo)*(.55))+.05

The only issue here is that any percentage of reduction down low becomes almost meaningless reversing the current problem (which isn't all bad).

Following that I feel the tattoo should keep the current method for calculating Endurance or adopt one that functions nearly identical to the RoBF magical reduction capped at 60%.

This effect is a percentage-based effect, meaning the largest tattoo in the game would reduce magic by about 25% as a RoBF; however, getting to 15% or 20% is relatively common. Unfortunately, it gets pretty hard to go up past that. To get to 30% would require being 6x larger than the largest tattoo.

This still does not solve much of the problems present as it still adds unnecessary PR as the tattoo grows. So, how about a TSA like effect - the minion with the tattoo equipped can regenerate 2.5% of HP up to its max trained HP. For the largest tattoo that would be around 650k a round which may be a little high.

That concludes my current thoughts - adopt an equation for endurance similar to the magic reduction of RoBF capped at 60%, leave the aura and SS effects as they are, and add HP regeneration.