I have got a few decks which I use for ELO, some with success and mixed results with others.
Now I'm gonna list a few of the decks I have used, any tips/suggestions or comments would be appreciated even if someone else has already said it!
Mono Skeelz (Works well surprisingly!)
And the new edition of Dr. Falkenstein
There are some obvious falls with a few of the decks!! any feedback would be helpful.
Out of these I would say Jungo is the best.
Skeelz are very good too although I'd personally use Chiara or Andy Ld over Zeke.
Mono-Nightmare looks great although lacking in power making some match-ups very tough.
Mono-Pcats look find, although they would obviously suffer against SoA or SoB match-ups.
Mono-Roots is usable but I'm not sure if it's the best choice as of now.
Half-decking is easier, IMO. In Mono you will find that each clan has a weakness of some kind... Too many low-damage draws vs SoB or SoA, not enough round-winning power, etc. Playing with 2 clans offers the opportunity to create a deck with more well-rounded draws. However, it's best if your cards can survive without bonus.
P.S. Phyllis is a 3* in a 2*s body that doesn't require revenge. Compare to Praxie (she may not have min 0 like he does, but the power difference and higher min is compensated by the more versatile SoB, which also protects ability vs GHEIST and Roots.)
Phyllis is a really nice 2* but its utility drops towards the end of the battle (So both Mawpin and Phyllis have a certain extent of restriction on their usage, maybe Phyllis has less). But I agree with ghelas that she is a really good choice for a Nightmare ELO deck. It's a matter of preference.