Each successive tier is unlocked by defeating each duelist on the lower tier a certain amount of time, i.e Tier 2 is unlocked by beating all the Tier 1 Duelists twice
It will so obviously not be coming back anytime soon (because Scry exists, because Surveil is semi-specific in flavor, and because Ravnica guilds usually dont reuse mechanics when they return
It gives all creatures you control +1/+1 until end of turn for each experience counter you have, and all your cute little Eldrazi Spawn and Scion tokens will get indestructible and annihilator 1 (whenever a creature with annihilator attacks, the defending player has to sacrifice a number of permanents equal to the annihilator value)
It also has some upside against various black commander decks or eldrazi with annihilator
World Championship 04 - 2004 (NA) Both Slate Warrior and Cipher Soldier (Kinetic Soldier) saw decent play for their mix of utility and stats
Theyre free spells that have a major impact on the game, and sometimes need to be removed to lower the power level of the deck