So Monday evening the girls whipped up a four-PC party covering the four 4e roles and all four power sources. They brought to the table:
A goliath warden
A gnome bard
A longtooth shifter ranger
A deva invoker
We got through one encounter: the sample encounter I whipped up for the beelion (3 kobold skirmishers and a beelion). The map was Dwarven Outpost from the Miniatures Game Starter Set, with the fight concentrated around one of the corner start areas as the bad guys came at them from ambush. The bad guys won initiative and used all their shifting abilities (the kobolds' shifty and the mounted beelion's guided frenzy) to surround the party and get some hits in on the softer targets (the bard and the ranger).
The gnome used fade away to get clear and the invoker slowly backed off as the warden marked almost all the enemies on the field and pulled the mounted kobold off the beelion. The beelion used lion's frenzy to get another hit on the ranger even while marked. The warden soon managed to mark all four enemies at once and got hit by all four for lots of sneak attack damage for her trouble. Impressively, she was still standing. After that round the PCs' attacks started taking a toll and kobolds started to drop. Unfortunately, the beelion's alluring gaze dazed the warden, leaving her unable to get out of the blast area of the invoker's next attack, and that coupled with more hits from the kobolds managed to take the warden down. After the warden had failed one death save, the last kobold (4 hp left) mounted the beelion (11 hp) and they flew away.
I need to make two small tweaks to the beelion. The alluring gaze is way too powerful to be at-will. I'll make it recharge 5 or 6 and drop the attack bonus by 1. Since I don't want two recharge powers on one monster, and lion's frenzy is only useful in specific circumstances anyway (next to 3 or more foes) I'll make that one at-will. The updated stat block is below:
Two other things I took away from this fight:
1) Goliath wardens can soak sick amounts of damage.
2) Maxed-Cha bards make clerics and warlords look like healing amateurs.