What is the best 15 card sidedeck for any deck? I need to know i am going to nationals

Its kind of hard to suggest a side board if I dont even know what is in your deck, but here are some cards to think about:

Des Wombat-the ultimate counter against burn
Mobius the Frost Monarch-good for eliminating stall cards
Ceasefire-Helps against Tsukuyomi+Magician of Faith tactics
Kinetic Soldier-good against warriors (obv.)
Dust Tornado-I never main deck this, idk why
Royal Oppression-Goats, Chaos, Zombies.

Kinetic Soldier
Barrel Behind the Door
Barrel Behind the Door
Mobius the Frost Monarch
Mobius the Frost Monarch
Swarm of Locusts
Divine Wrath
Royal Opression
Royal Opression
Magic Drain
Magic Drain
Then 4 cards that you were going to deck but got rejected by a tough choice.

-Dum Manz Groop

There is no best 15 side deck cards because there's no way to counter against ALL the kinds of decks in existence. It's best just to go with your gut instinct. Ask yourself what types of decks are used the most in the area and what types of cards can counter against multiple types of decks.

Death/Des Wombat, for example, is a good counter for Burn AND Stall since it's level 3 and its effect reduces any effect damage you take to 0.

post ur deck then ill post what i would suggest for what u have in there as a side board

There is no best 15 side deck cards because there's no way to counter against ALL the kinds of decks in existence. It's best just to go with your gut instinct. Ask yourself what types of decks are used the most in the area and what types of cards can counter against multiple types of decks.

Death/Des Wombat, for example, is a good counter for Burn AND Stall since it's level 3 and its effect reduces any effect damage you take to 0.

thanks for the help here is my deck if it will help

tribute monsters
1xjinzo
1x hades
1x blowback
1x dmoc

4 star of lower
3x strike ninja
3x d.d scout plane
2x zomrya the dark
1x don
1x mystic tomato
1x tribe
1x sinister serpent
1x breaker

magics
1x pot of greed
1x graceful
1x mst
1x heavy
1x snatch
1x preamture
1x card destruction
1x lighting vortex
1x dimension fusion
2x creature swap
2x scape goats
2x reinforcements of the army
2x smashing ground

traps
1x call
1x ring
1x TT
1x waboku
1x ceasefire
2x sakretsu armor

i hope that helps thanks guys