After playing this game for little over 3 years. I have come to a conclusion about halfway in... "Bloodlust is more of a liability than an asset". Think about it, more and more players are developing strategies to counter this buff. You can't do it vs UD unless the player is an idiot and doesn't know what Devour Magic does. Spell Breakers can steal it and SW/Priest can mass-remove it. NE could just turn the autocast against them with Faeries or remove it slowly with Dryads or mass-remove with 1 Wisp.
I mostly use it if I can get a upper hand on my opponent (wore him down) or I am in a team and I want to assist t3 air by adding a little more "punch" to thier 60+ dmg attacks. And even then, I still prefer the effects of Purge and LS.
Purge is like the "Magic Ensare". In sense it stops the unit dead for a few seconds and they regain speed. It also smashes summons which should be a necessity when you fight things like Firelords, Beastmasters, and any other summon based or summoned unit. Plus it gets rid of the annoying de-buffs.
LS is just funny. If you plant it in enough areas, you could weaken up an army to a point where some of the units are actually easy to kill. Try doing this in TP ins. Especially if the base design doesn't work for them. But then again, its a double edged sword
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Cause really, there is more to ANY caster than just their Master Spells.