Does the Pack Tactics monster special trait really only apply to one attack roll?

Question

I am adjusting the stats on the sea lion from Tales From The Yawning Portal to build a lower CR sea lion cub and its pack tactics special trait got me wondering.

The trait reads (additional emphasis mine):

Pack Tactics. The sea lion has advantage on an attack roll against a creature if at least one of the sea lion's allies is within 5 feet of the creature and the ally isn't incapacitated.

To contrast, here is the sahuagin's blood frenzy special trait:

Blood Frenzy. The Sahuagin has advantage on melee attack rolls against any creature that doesn’t have all its hit points.

It seems more clear to me that the sahuagin's ability applies to multiple attacks.

Does this mean that the sea lion can only use this ability on one attack on each of its turns?

Does it also mean that pack tactics could only benefit an attack on the sea lion's turn or an opportunity attack but not both?

Answer 1

If there are 1/turn or 1/round limitations on a feature, it is always explicitly called out (see the stat block of the assassin on DMG 343). Here it means the same as "the attack roll" or "attack rolls" would. In other words it applies to all attack rolls when the conditions are met.

Answer 2

Usually when things are limited to once per turn/round/rest they explicitly say so and usually begin "once during your turn" or some such. "An Attack roll" refers to any action that requires a roll for accuracy, including melee weapon attacks, ranged attacks, magic attacks (except magic missile and those that require Saves from the target), and natural weapon attacks.

In this case both the bite and claw attacks of the sea lion required this roll as they are "Melee Weapon Attack: +5 to hit" so they gain the benefit from the pack tactics trait.
Since you would be using one of these as their attack of opportunity they will gain the benefit then also. Basically every time the Sea Lion attacks when a conscious ally* is within 5ft of target they get advantage.

*note that it says ally for this one whereas for sneak attack it says "another enemy of the target" so make of that as you will.