If you know you can't participate succesfull, save your resources. I wrote the following in a similar thread some days ago:

"It is possible for f2p players to get in the first places, if you don't try in every tournament. I wanted to get Yoshi at the last fragment summoning event. I saved my resources (especially shards) before it began, didn't use the sacred shards from monthly quest immediately. I got Yoshi, and won the "Champion Chase" (my group, not worldwide score list, of course). I used all my shards, including 1000 mystery (very annoing to do such a summon rush, the vault is much to small), to do that.

I did all event stuff, but at most stuff I stopped when reaching the Yoshi fragments. Only one dungeon I did until top 10. I bought xp-boost for jewels in the market (champion training event) and spent a lot of jewels for extra energy. In addition to that I saved all my energy from free reward chests for a couple of weeks. They last for 99 days, you don't have to use them the day you get them.

I got my Yoshi and a 6* Relentless set. I didn't spent any real money during this event. Now I'm out for the next two or three events, saving my resources until I can participate successfull again."

Maybe I trie to get one for the epics now, Malacai, his AoE hp-burn looks great for Spider dungeon. But I'm not going to invest in this event beyond that.

Yes, fusions are extremely tough if you can't do the dungeons at a higher level, ideally stage 20 but at least 16 or so. Arena events are normally supposed to be the easy part, but they may still require a lot of refreshes indeed, considering the current difficulty of arena. But the biggest roadblock is generally the champion chase / summon rush - unless you have a huge stockpile of mystery shards like veteran players do, you'd need to have enough shards / fusions ready to go. 

That being said, you may want to see if you can get one or more of the epics. The champion chase and summon rush are focused on Skimfos and Mordecai, so you could ignore those events completely and still get the other two epics, Fenshi and Giscard, or at least one of the two. And each of the four epics seems to offer at least some use to newer players. 

Not only you have to save enough gems + shards + energy + x2 exp, but also you have to complete all dungeons at last levels to play fusions. Without them, please don't join any fusions. Remember fusion is design to suck players dry, not you, but all old players. 

I think it will be incredibly difficult for you with only 13 cleared.

Dungeons shouldnt be the problem, even at 11. might need optimal play and some gems but its not a real hurdle

Arena might be your real problem as I think Bronze 4/ silver 1 is needed realistically, Bronze 3 perhaps too

and ofc Champ Chase and Summon Rush those 2 are the hardest for F2P/low spender.

Best preparing for Summon Rush as f2p is to buy every green shard you see on the market. If a Champion Training is at the same moment, you can feed them to each other after summoning, maybe level up once before to get the points from the first levels. Choose some that get feeded up to next rank. Like I wrote before, I used a thousand green shards at the Yoshi-Event.

I'm in a similar boat.  I've been saving and prepping ever since they announced this and then they come out with the schedule and it seems (so far) to be harder than previous events.  I'm going to try for it and I'm in a slightly better situation than you since I'm a bit higher in the drag and arena... but fireknight might be impossible for me.  99% of the reason I want this champ is for help with the fireknight where I have literally half the progression than in any other dungeon.  I have a couple of 3 hitters at 40 that I guess I could level if I have to although I really hadn't wanted to invest in them.  But you need to get every single fragement from every single event (since winning the tournaments is laughable... that's not a real suggestion unless you are talking to an atm).  I don't know, it is a bit disenheartening.  This was going to be my first fusion which looked doable with prep and a ton of effort after Yoshi.  We'll see.

This fusion is really disappointing, I spent many many hours preparing for this event and not a small sum of $ too but its been placed out of reach of myself and many other people.  Fix it and do better in future please Polarium.

i  hear  you  and  am  a  bit  torn.    I  was  thinking  about  chasing  fenshi  and  giscard  but  am  thinking  it  will  absolutely  wipe  out  my  silver  and  gem  stores.

i  think  fenshi  could  help  me  but  it  reqires  2  training  events  Which  combined  with  the  dd  and  dungeon  runs  will  be  way  more  enery  than  i  have  saved  up  restores  for.

two  of  the  others  requrire  arena  which  has  been  a  real  struggle  for  me  tbh.

end  of  the  day  i  might  just  try  for  fenshi  and  move  on.    Would  be  a  shame  to  blownthrough  all  the  resources  for  giscard  only  to  fall  short  because  of  arena...

If  i  could  i  would  try  and  get  Fenshi  and  Mordecai.  Skimfos  looks  interesting  but  situational.  Giscard  just  looks,  well,  average  after  his  nerf.  I  wish  I  could  have  gone  for  a  couple  of  the  epics  but  went  for  Brogni.