Im sitting on 14k gems right now, and wont spend it until dragon masters come in January. I for sure try for Cynthia. She can rise her attack, speed and crit chance (you can check it on dev video), and have powerfull 3 bar move. If her stats will be decent she will be monster. And best ground striker for sure.
Depending on Lance skills and stats could spend some gems on him. For example if he would end up with being support: with potion and hight damage hyper beam he just need tanky stats, and some sick trainer move. Im dreaming about +acc all (with maybe speed or crit or move gauge), because miss with hyper beam will be tragic. Also my first game was PGold, and I didnt play black and white (i play it currently on emulators) so nostalgia is on Lance ;)
I dont really care about Christmas banner. I dont like sesonal skins that much in general, as I said Im just playing B&W so dont have feelings for Rosa, like many people do, and X&Y E4 was so weak that I dont even remember them. Delibird is stupid pokemon, and he is similar to Oshawott (who is better in my opionion, and will get evolution). Octillery is pretty good, but I would prefer Feraligatr that is now in banner. And Liepard have nice gimmick, but is is not worthy being 5* in my opinion.