Though the "Killer Effect" is an established game mechanic in FFXI, I'd like to suggest changes based on "thematic" principles. These changes would affect Beastmaster vs Blue Mages, specifically. Paladins, Dragoons, Darkknight and Samurais would NOT be affected by the following changes.
Firstly, Beastmaster's "Killer Effect"(10%/cap50%) is an intimidation effect. This thematically seems the complete opposite of what a Beastmaster is. If we follow the storyline, "The chocobo abuser", then it's wrong to treat pets badly.
I think a more appropriate ability would have been, "Beast affinity". "Beast Affinity" would increase a player chance(same 10%/cap50%) to charm a specific animal family group. Also, would add a bonus against opposing mobs family. As with the regular "killer effect" each "Affinity" would be tied to specific groups.
The mob themselves could retain their regular "killer effects" since this is a product of genetics and "Survival of the Fittest."
As for Blue Mages, everything about them is geared towards aggression and intimidation. BLU's are appropriate candidates for "Killer Effects"(8%/cap 50%). While a BST's "Affinity" would be geared towards a defensive ability, BLU can keep their offensive effects. Also, as we approach lvl 99 we should gain the remaining "Killer effects" as BLU job traits via spell selection.
Finally, if player don't feel like touching the original "Killer Effects", I think the argument could be made for Bluemages receiving a higher tier of "Killer Effects" based solely on "stacking" like-family spells. For example, most BLU "Killer Effect" requires 2 family moves...then, having 2 additional family-moves(4total) would give BLU's 16% "Killer Effect". Or alternatively perhaps BLU could acquire a "cap break" increasing cap to 60-70%.
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As an aside concerning "Killer Effects"...
... perhaps it's time for SquareEnix to address the new family grouping(luminorian, elementals, etc) NOT originally included in the beast charts...
...Isn't it time for SE to create a beastman vs Beastman "Killer Effect" chart? With this BLU can at least gain a bonus against beast man clans...
...also, Are Automaton considered Arcana? If they are, shouldn't they receive the "Undead Killer Effect"?