Whenever you gain life, you may put a +1/+1 counter on Ajani's Pridemate.
11/17/2017 The ability of Ajani’s Pridemate triggers just once for each life-gaining event, whether it’s 1 life from Auriok Champion or 6 life from Tavern Swindler.
11/17/2017 If Ajani’s Pridemate is dealt lethal damage at the same time that you gain life, it won’t receive a counter from its ability in time to save it.
11/17/2017 Each creature with lifelink dealing combat damage causes a separate life-gaining event. For example, if two creatures you control with lifelink deal combat damage at the same time, Ajani’s Pridemate’s ability will trigger twice. However, if a single creature you control with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will trigger only once.
11/17/2017 In a Two-Headed Giant game, life gained by your teammate won’t cause the ability to trigger, even though it causes your team’s life total to increase.