It's the way of any Warhammer 40K player, really. When I was a child ... This is how I ended up with a company of Dark Angels, complete with transports and HQ options, but also a unit of Sanguinary ...
When I opened up the new Warhammer 40K Kroot Lone-Spear ... I used a Hand Flamer and head from the Blood Angels Sanguinary Guard kit, which I had various parts of in my bits box, and hollowed ...