Does this solely rely on one's astral power relative to the opponent? I build a pretender (monolith) with 2 astral and am now afraid that some of the races with astral ability will be able to take him out with sheer numbers of cheap astral mages (lvls 1-3). Does magic resistance, hit points, pretender status, or anything else factor in? I should win on any of those counts quite handily...
On the other hand, to mind duel your pretender, they would have to be storming your capital. Which mean you either made a big strategic mistake, or you are losing anyway.
So, don't leave your capital undefended, and make sure you're not losing, and you'll be all right
There's a random factor in there too. A 2 astral mage wont always lose to a 3 astral mage, for example. Anyway, a stationary monolith inside a castle is pretty much safe.
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So I take from this that (a) its astral on astral, no questions asked about anything else including magic resistance, (b) putting astral on your pretender should be an all or nothing (or at least carefully considered), and (c) suicide attacks against a tough opponent like a monolith make sense because with 480hps and a 32 protection, they are nigh invincible through other means.