The Paladin might have a duelling ability that triggers when he is attacked. I Imagine: If the Paladin is successfully attacked by a creature that is of a higher level than 2, place a challenge token on that creature. Whenever the Paladin makes a melee attack against a creature with a challenge token on it he gains "Melee+1" and "Piercing+1"
This benefits theme and playstyle because he is that active fighting mage without being forced to be a solo mage. Themewise level 3+ assures that he only feels challenge by bigger things like mages, dragons, trolls and makes him a bit more vunerable to swarm builds. Succesful attacks distinguish him to the forcemaster who is all about avoiding incoming attacks - this does not seem appropriate to a paladin!
I could see alot of Paladin-Equipment being build around those Challenge tokens, like a shield that allows you to place a second and adding armor/counterstrike or a war Enchantment that lets him place taunt markersto ensure that he is being attacked by creatures of his choice. Something that lets him replace said tokens or gains him even further buffs with challenge tokens!
This abillity would be really cool because I am a bit sick of "pet-abilities" and this would be more like the new warlock with an external ressource played on the enemies creatures.
For the Siren "flood markers" are not very fullfilling and are to similar to the druid. I guess the terrain subtype will greatly affect the way she playes but not as much spreaded as the vine markers are. Maybe she sets a spawning pool where all of her creatures come to land? Probably she can form water, thus freezing people, making use of airspells too? Be a master of the weather and buffing creatures that fight under rain/storms? I feel that my paladin ideas are much better
