I don't remember unpacking this one, i just found out recently when i was trying to build a sleep deception deck so instead i switched to building a guild deck with Merrick

list

you will notice that i don't run Desert Mercenary nor the hollow and my reasoning is very simple it's because i don't own them,
it's mostly guild creatures with buffs and hidden and some reactive cards
i always keep Frumentarii in mulligan and then look for any low cost creatures with hidden, patient pickpocket works but it usually gets removed by magic/death turn 1

this deck is FAST or at least it can be, depends on the draw and matchup, the match can finish as quick as turn 4

there was a way for him to prevent lethal for a turn but he missed it.....

Cool Combo

it's worth mentioning cause it popped off alot you buff a creature with selfless guildmate and then you give it deadly next turn with uncanny rogue and now the 1/1 body that no one cares about has deadly and can trade with your Valewarden.

So Merrick.....

his neither a win con nor a win more he fits with any hidden rush deck drawing him on curve is crucial but keeping him in mulligan is questionable,
i think he works better in a midrange deck where you can have merrick with or without your buffed creatures for him to work

What to avoid

1. i see no reason in keeping merrick in mulligan so avoid that
2. attacking without the buff is bad in most cases so avoid that
3. using buffs on merrick defeats the point so avoid that

and this concludes my impression on merrick see you next time!