Hmm I guess this is probably the best place to detail the mechanics for them. Entei, Suicune, and Raikou are now more commonly found if you have certain abilities in your party.
For Raikou those abilities are Lightning Rod and Volt Absorb.
For Suicune those abilities are Storm Drain and Water Absorb.
For Entei those abilities are Flash Fire and Blaze Boost.
These abilities stack with one another but each ability does not apply more than once. The equation for determining the probability (%) of discovering one of them on each encounter is:
Where a1 is 1 if the first ability is present and 0 if it is absent,
And a2 is 1 if the second ability is present and 0 if it is absent.
Examples:
Having 0 Pokemon with the above abilities would give you a ~1.7% chance of finding any of the Pokemon in question.
Having 1 Pokemon with Storm Drain in the party would give you a ~2.9% chance of finding Suicune.
Having 2 Pokemon with Storm Drain in the party would still give you a ~2.9% chance of finding Suicune.
Having 1 or more Pokemon with Storm Drain and 1 or more Pokemon with Water Absorb in the party would give you a ~10% chance of finding Suicune.
For comparison, the rate was ~1.7% on the previous patches.