Just learn from the big (wizard, who invented card games with creature).
The System has a stack order. This avoids that effects trigger two times (or even more). It also is important for trigger to trigger in the right order. It is no problem, that magic uses mana and many creatures and eredan does not use mana and only 3 fix creatures, because the problem to deal with the trigger order is the same in bouth games.
Most bugs with bonus on status-values and most bugs which leads to double damage or double heal may depend on the lack of an clean programmed stack oder or if there is such a system a bad implementment of new cards or reedited new effects into that system.
So learn from the big card games and use a stack order system and implement the cards clean in the stack order system. This should avoid most bugs.
http://www.essentialmagic.com/articles/thestack.aspor explanation as video:
https://www.youtube.com/watch?v=k-9k5pf9Uc8Also always search for all the old cards with that name (including collecters edition) and connect them with the new in the right way. Bugs that still happen:
- old and new card have different loads [like actual old 10 loads and new 9 loads]
- old cards cant be played [like old version lv 4 ice border]
- old and new cards can be played doubled = like same char 2 times / same other cards 6 times
- collecters edition of a rare card / legend card does not count for the new Quilingo limitations [/ / ] (this one might be tricky, but has to be fixed)