Blackmantle
King
IMO, its not an exploit if there is no alternative...
All units should have thier counter... and Mobility II assassins cannot be caught 'on the counter-attack', as they have 3 movement! The only counter to assassins, are Guardsmen (or Royal Guards), and those are only rarely available.
I would rather have a horribly expensive national unit that is always available, and is very weak, than workers. But since none exist ATM, I will have to use the 'exploit'
But Assassins should be guaranteed which target they will be up against... its nasty to be shouted "SURPRISE, you aren't going up against the lvl 10 Archmage... you are going up against a lvl 15 Hero!!". As a result, 50% is FAR too low...
Heres another idea to consider... a "Protector" Promotion.
Available to Melee, Archery, and Recon units.
Requires Combat III
-100% Strength (With Combat III this gives a final value of -40% of the base strength)
Doesn't gain XP from combat (Use the withered promotion effect, but with -100% instead of -50%, if possible)
Intercepts Marksman Attacks
If it whould be "just" hawks and (edit due to typo: )workers one could argue that one to a certain (since hawks are somewhat limited by slots and workers are expensive) but since slaves work just as well and are even more odd as targets chosen by assasins for assasination its very cheesy. (you can get many slaves from slavery civic + barb-hunting or from slave trade via the undercouncil civic / resolution.). Using that can yield you like 10 - 20 "meatshields" easiely and cheaply. And those are hard to bypass even by blitzing assasins.
Hence i restrain from using either. Especially since the AI whould not pull something like that off.
I whould very much like a late game-low strength high-cost guardsmen for all civs as well. (perhaps as a national so you con't spam them / make your mages untouchable.) With Marksmen-Units bypassing noncombats just like all other units (including greath people but perhaps not ships if thats not to much of a problem codewise.).
Perhaps a spell in one of the new spheres or a relocation and an addition in shadow-magic like suggested by xienwolf might be fine as well..
Main problem with hawks having that ability is that they perhaps are already one of the most powerful and underpriced units in the game with all they offer. Add that one in and they are insanely strong against nigh anything exept places where brute force is needed alone. But there is more than enough to take care of that allready.