Licia, Sanguine Tribune — ruling 1

Licia's first ability reduces only generic mana in its cost. It can't reduce the cost below {R}{W}{B}.

Licia, Sanguine Tribune — ruling 2

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.

Licia, Sanguine Tribune — ruling 3

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.

Licia, Sanguine Tribune — ruling 4

If Licia's last ability doesn't resolve once activated, it can't be activated again in the same turn.

Licia, Sanguine Tribune : règles, fonctionnement et interactions (MTG)

Licia, Sanguine Tribune is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

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.

How it works : Licia, Sanguine Tribune

Original English text — Wizards of the Coast / Scryfall

#1August 25, 2017· Wizards of the Coast
Licia's first ability reduces only generic mana in its cost. It can't reduce the cost below .
No other card is named in this ruling.
#2August 25, 2017· Wizards of the Coast
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.
No other card is named in this ruling.
#3August 25, 2017· Wizards of the Coast
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 less to cast.
No other card is named in this ruling.
#4August 25, 2017· Wizards of the Coast
If Licia's last ability doesn't resolve once activated, it can't be activated again in the same turn.
No other card is named in this ruling.