If you have multiple Mystics and build multiple Obelisks or Snaking Sands, the Empowering Blasphemy, Sandstorm Warriors, Serpent God's Protection spheres are stacking. This looks fine in a 4 player map for the buffs are mostly distributed between all players, in a single player map it actually can lead to insane high damage numbers.
The stacking is always on top of each other which makes the HD/AP increasing fast into millions, meaning that you can 2x,4x,8x,16x,32x,64x,128x,256x,1024x,2048x your whole HD/AP (if you receive enough shields fast enough you can get millions of HD or AP). My highest HD i had was on my Gunwitch with over 1m HD and she hit over 20m per auto attack (4 obelisks and some other buffs). This can be used on any hero leading to really strong attacks on any of them.
The stacking of the damage reduction always takes the new def value as a max, which reduces it's effectiveness with each stacking. This makes it really hard for monster to actually take down any wall with a few Obelisks around. It actually can turn even any Obelisk into an really strong wall by just placing them next to each other around a Core.
Same like for Obelisk, the Sandstorm Warriors is stacking, this leads to an slight increase of HD/AP the more Sandstorm Warriors are active around the Hero, also the Damage reduction stacks from it with dimished value the more Sandstorm Warriors are active.
I honestly think the stacking is fine in multiplayer, it just looks really strong in single player for you receive all buffs on one character. I also think if the stacking is intended it should just add the base value instead of stacking all buffs on top of each other, this would need a whole system change on how buffs work though. Maybe of stacking the buffs get just the timer refreshed.
Steps to reproduce:
The buffs don't stack :_( and just refresh each other.