Arena:
Thoughtspore - Redirect
Necropian Vampiress - Critical Strike (or Falcon Precision if vs. Defenses)
Thunderrift Falcon - Gator Toughness (or Lion Savagery, esp. if "Pet")
Any Straywood Beastmaster "Pet" of Level 2 or higher - Joined Strength
Any Arraxian Crown Warlock "Blood Reaper" - Demonic Bloodlust AND Demonic Link
Goran, Werewolf Pet - Demonic Bloodlust (and often Vampirism)
Ehren, Enduring Paladin - Regrowth
Knight of the Red Helm - Knight's Courage (probably the most obvious in the game)
Naiya - Harmonize (and Brace Yourself and Glancing Blow... basically if you're going to Harmonize her, you've just made killing/protecting her the focus of the match)
Big enemy creature - Song of Love or Chant of Rage (depends on Mage training)
Armoured enemy creature - Rust
Regenerating enemy creature - Theft of Life
Domination:
Level 1 living creature - Panther Stealth
Tarraki, Thousand Bites - Badger Frenzy (this is borderline broken)
Guardian Angel - Sentinel of V'tar
Enemy living support creature (like a Standard Bearer or Redclaw or Guardian Angel or Wychwood Faerie) - Plagued
Enemy level 1-2 guard - Shrink
Sslak that an enemy is trying to take out - Giant Size
Usslak I'm trying to take out - Rust or Agony or Tangleroot (depends on Mage training)