as theres no trading aspect to MTG Arena, which is a big aspect of physical MTG, the need for wildcards becomes immediately apparent
[2] Once per turn, if you control this Normal Summoned card: You can Tribute from your face-up field, this card and 1 non-Tuner monster with a Level lower than this card, and if you do, Special Summon 1 Synchro monster from your Extra Deck whose Level equals the difference of the Tributed monsters' Levels, then you can destroy 1 card your opponent controls (this is treated as a Synchro Summon)
Also, as mentioned above, once either player plays a Counter Trap Card, no other card or effect can be chained except more Counter Traps
Instant speed Double Strike can kill, so play safe
Heres where the problems start
8 Norn's Choirmaster There are many cards that depend on you controlling your commander to gain some type of benefit, but few are quite as good as Norns Choirmaster