This appears to be one of the most under-used tattoos, and has been as long as I can remember, and while there have been many suggestions on how to improve it (http://www.carnageblender.com/bboard/q-and-a-fetch-msg.tcl?msg_id=003C8H) I thought we could discuss this again.
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:
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 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.