Sentinel's Mark
Enchantment — Aura
Flash
Enchant creature
Enchanted creature gets +1/+2 and has vigilance.
Addendum — When this Aura enters, if you cast it during your main phase, enchanted creature gains lifelink until end of turn.
Zezhou Chen
Ravnica Allegiance (RNA)
• #20Rulings
Multiple instances of lifelink on the same creature are redundant.
(wotc • 2019-01-25)
If an effect copies a spell with an addendum ability while it's on the stack, the copy wasn't cast at all, so you won't get the addendum bonus.
(wotc • 2019-01-25)
Gaining vigilance any time after the moment you choose to attack with a creature won't cause it to become untapped, and losing vigilance after that time won't cause it to become tapped.
(wotc • 2019-01-25)
If Sentinel's Mark enters the battlefield without being cast, the addendum ability won't trigger, even if it's your main phase.
(wotc • 2019-01-25)
Rulings
Multiple instances of lifelink on the same creature are redundant.
(wotc • 2019-01-25)
If an effect copies a spell with an addendum ability while it's on the stack, the copy wasn't cast at all, so you won't get the addendum bonus.
(wotc • 2019-01-25)
Gaining vigilance any time after the moment you choose to attack with a creature won't cause it to become untapped, and losing vigilance after that time won't cause it to become tapped.
(wotc • 2019-01-25)
If Sentinel's Mark enters the battlefield without being cast, the addendum ability won't trigger, even if it's your main phase.
(wotc • 2019-01-25)