I've started to DM campaigns on Discord and I like creating my own boss monsters based on sheets I find,and them changing them to suit what I want. Right now I'm working on a ice themed Undead encounter based around the Frostfallen idea I found. Anyhow I'm trying to decide what legend actions to assign to my Wight Tyrant boss,and I'd at a loss,as Discord limits my actions,as we mainly don't use maps,so I have to describe everything to my players,which rules out terrain altering or anything like that. I'd rather not barrage my players every turn with abilities,as they are going to be fighting his minions and summons as well,so any ideas on what I could give him? I did plan on giving him some kind of ability to summon more minions via summons and some kind Of Ice Spears as the location is a giant Ice cavern,but apart from that I have no idea,as the boss in question is going to be distracted by trying to summon something rather nasty when they burst in.

Perhaps the ability to whip up a blizzard that makes ranged attacks disadvantaged? Maybe dip into naruto style and let him have ice mirrors he can create around the room and travel/attack through? Final thing could be decreasing the temp exponentially and the players either have to pass con saves to not be frozen or have some way of keeping themselves warm? Just a few spitball ideas there