VTxCT = messy tailed VT. Combtail is CTxPK.
CTxHM = initial messy tails. Uneven form, difficult to accomplish the full potential of a halfsun.
CTxDT itself is hard, as focusing on the DEFORMITY (Dt is not a tail type moreas it is a deformity...) of the DT, trying to keep the fry alive (trust me...) because they are weaker and short bodied, and then add in the possible mess of CT. Throw in an DTHM, you worry about the full spread, the even lobs VS getting mitten tails, and the rays of the crowntail.
CtxDeT will be like HM, because you want to still focus on the form of the DeT, while keeping the CT look uniform and not messy....
Have you bred before? Ever? The tail type crossing you are mentioning are VERY difficult and time consuming. You have to breed F1 onwards, to gain any potential good looking fry. I say try with CT x CT first, try to get a strong good looking line going then add in some other tail types as you advance.
Dragonscale x regular betta = metallic, or regular. Dragonscale is a double metallic... Whereas metallic is a single, and regular is none. If you crossed dragonscale to dragonscale, you get dragonscale and metallic. Cross to metallic you get some dragonscale, mostly metallic and regular.
ELEPHANT EARED BETTA
Though it has been said it is recessive and only 10% or less of spawns gain that aspect, there are those who have bred and had 30%-70% who have the big eaed look... Usually you will get larger pectorals than usual, crossing an EE to any regular. Cross EE to EE you will get 50/50 chance.
Halfmoon females must have a D shaped caudal, or more than (over halfmoons).
HMPK will have a shorter smaller caudal, plus their anal fin will be straight, and NOT swoop under their caudal whereas halfmoon can swoop under. HMPK will also have a short anal fin.
ROUNDTAIL is just a variety of the veiltail. Literally, round, is their tail shape. Their anal fin will be that of any veiltai... long and swoops under the caudal, which will be larger. Veiltail females have longer caudals as it is.