From a gameplay standpoint, this set offers nothing new
The card synergizes with blink effects like Ephemerate and Teleportation Circle, letting you rack up counters faster
The Seriema doesnt make itself indestructible, so give it hexproof as soon as possible
If you do yourself and average of 0.33 damage a turn and your average game takes 6 turns you can assume your life total is closer to 18 than 20 in reality
Karlach, however, is more useful in Commander than in anywhere else, while Jaheira has more use cases elsewhere
(If this creature isn't monstrous, put X +1/+1 counters on it and it becomes monstrous.) If Maester Seymour is no longer on the battlefield when its first ability resolves, use its power as it last existed on the battlefield to determine how many +1/+1 counters to put on the target creature