It is near impossible, unfortunately, because most of players are more experienced and have better armies (well, in current situation, almost every army is better than seraphon if built and played properly). But I can do it if I go 3 out 5 wins. This would be equal to winning an event in current meta.
There are 3 DoK players with almost absolutely equal lists - Morathi, Slaughter Queen on Cauldron, 70 witches (some replace them with sisters of slaughter), 10 kinerai and 2 hags+cauldron guard. Others are 2 stormcast evocators+sequitor spam and evocators + double ballista. 1 FEC with massed ghouls, one Khorne player who won the previous tournament, single sylvaneth with treemen, couple of CoS lists, single skaven with 80 plague monks and 9 jezzail, single Ogor player with 4xStonehorns.
Most feared of all - Fyreslayers player who ended up in top 3 in one of GTs. He is bringing 30+10+10 Hearthguard berzerkers, 5 aurics, runefather, runesmiter on magmadroth, battlesmith and runemaster+lords of the lodge. Honestly, I don't have a slightest idea how this list can be beaten with dracotion's tail (or any other seraphon list). It looks too durable for alpha-strikes, it is fast enough to grab objectives, it kill anything that we can throw at it and we can do very little damage to it.