There are probably 100 new mechanics they could add. Here are 20 samples:
ImmobilePenalty- Ranged damaging spell drops a circle on the group which lasts ~5 seconds; enemies in that circle take 40% less damage from you.
BeVehicle- carry teammate for long travel / mobile shooting
AntiburstTank- convert 50% of incoming dmg to a slow DOT
MountedCombat- fight atop a generic mount (creature, not carpet/cycle) which helps you attack. Being damaged doesn't dismount you, but dropping to half health knocks you off and the mount runs away until you earn it back.
AblativeDps- your dps is reduced as your hp go down, making it less important for enemies to finish you off.
RetrieveYourStuff- ranged spells drop something on the ground at target, which you can retrieve to cast again faster.
SolidShield- block autoattacks on teammates behind/beside you.
PersonalScavengerHunt- Small items are scattered pseudorandomly through the map, which you can collect for bonuses.
Nonthreatening- enemy effects/attacks can't target you unless there is no other valid target in range (they'll snap to the other guy instead). Enemy effects that prioritize heroes treat you as less than a minion.
FastCantStop- You can move very fast, but once you stop it takes a long time to get up to full speed again.
FastCantRetrace- You temporarily leave a trail behind you that you can't return to, or you'll be punished (optionally invisible to others)
LoadBearingPet- you have pet/summon/clone, and when it is killed you suffer a major penalty (or even die)
AttachToTeammate- grab onto a teammate and use her position to cast your spells from. Damage to that teammate is partly split between you.
SuperfastRegen- low base health hp, but passive regeneration is super-high. (Optionally the healing is a bit lower when at lower health).
AntiFocusTanking- if more than 1 enemy is hurting you, only the highest damage (over a 1 sec interval) does full damage. The rest do reduced damage.
VoodooDoll- Target an enemy and spawn an object on the ground between you. Both teams can attack the object and eventually kill it; attacks from your team also damage the enemy you targeted.
DamageSilence- After 1 second of regular silence, for the next 4 sec your abilities will do hundreds of self-damage if you use them.
DamageRoot- For the next 5 sec, you take damage proportionate to the distance you move. (Movement by you, not external forces)
SeeThroughBush
HideNearBush.