Sorry for [MENTION=63746]Binder Fred[/MENTION]...
Shoving a target requires an Athletics check not an attack check and it is resisted by Acrobatics or Athletics, so the rolls are 1d20+2 vs. 1d20+2. I will use your 1d20 rolls at +2 until you knock it prone. So for round 1 its rolls are 12 and then 9 and if its is still up next round, 19 and 7.
Bessy
Hm, how about we try this:
Trip (Shove) attacks until it's prone (2 attacks last round, 2 this round), then regular attacks (now at advantage). Since it's already Grappled (movement 0), it can't get up until it succeeds in freeing itself from the grapple (at a disadvantage since it's Prone)
The ties that bind: 1D20+5 = [10]+5 = 15; 1D8+3 = [3]+3 = 6
1D20+5 = [7]+5 = 12; 1D8+3 = [7]+3 = 10
1D20+5 = [17]+5 = 22; 1D8+3 = [4]+3 = 7
1D20+5 = [5]+5 = 10; 1D8+3 = [2]+3 = 5
Must succeed at Str or Dex roll vs the above or become Prone. (I'll roll additional dice as needed, or you can if you want to, GK)
Shoving a target requires an Athletics check not an attack check and it is resisted by Acrobatics or Athletics, so the rolls are 1d20+2 vs. 1d20+2. I will use your 1d20 rolls at +2 until you knock it prone. So for round 1 its rolls are 12 and then 9 and if its is still up next round, 19 and 7.