No bankai level shikais. we aren't all old man yama
no free control over an element. if you are elemental, it will be separate attacks, like fire wall, or tornado ect
no time manipulation
no regenration for shinigami, and hollows, if you have enhanced regeneration, it can't be instant, maybe growing an arm slowly in battle, (relatively slowly)
healing powers, just like regeneration nothing extreme, even unohana doesn't heal instantly
dimensional powers, these are tricky, but if you do it very well i may allow it.
no illusions, unless it's very minor, and more like shinji's illusionary zanpakuto, no kyoka suigetsu
no stat boosting powers, unless you have a sufficient drawback.
for all powers, add your own drawbacks and usage limitations. don't spam one attack continuously like...ichigo. but attacks like renjis extending sword, spam those, because it's acceptable. also, if you have a godly technique powerwise, seriously put a limit on it, don't make me put a limit, because you won't like it if i do.