Licia, Sanguine Tribune
Legendary Creature — Vampire Soldier
This spell costs 
less to cast for each 1 life you gained this turn.
First strike, lifelink
Pay 5 life: Put three +1/+1 counters on Licia. Activate only during your turn and only once each turn.
"I give my blood, my life, all I have in exchange for victory."
Magali Villeneuve
Commander 2017 (C17)
• #40Rulings
Licia's first ability checks how much life you've gained during the turn, not what your life total is compared to what it was when the turn began. For example, if you start the turn at 30 life, gain 6 life during the turn, then lose 10 life later that turn, Licia still costs {6} less to cast.
(wotc • 2017-08-25)
Licia's first ability reduces only generic mana in its cost. It can't reduce the cost below {R}{W}{B}.
(wotc • 2017-08-25)
If Licia's last ability doesn't resolve once activated, it can't be activated again in the same turn.
(wotc • 2017-08-25)
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases (such as the "commander tax"), then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
(wotc • 2017-08-25)
Rulings
Licia's first ability checks how much life you've gained during the turn, not what your life total is compared to what it was when the turn began. For example, if you start the turn at 30 life, gain 6 life during the turn, then lose 10 life later that turn, Licia still costs {6} less to cast.
(wotc • 2017-08-25)
Licia's first ability reduces only generic mana in its cost. It can't reduce the cost below {R}{W}{B}.
(wotc • 2017-08-25)
If Licia's last ability doesn't resolve once activated, it can't be activated again in the same turn.
(wotc • 2017-08-25)
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases (such as the "commander tax"), then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
(wotc • 2017-08-25)