There is a special ruling that this effect will always add 100 in any case, and in terms of combat, it boasts a high level of perfection that you wouldn't think it was 10 years ago
Outlaws Merriment, for example, gets very confusing with Far Out since theres no answer for what happens when all three modes are pushed into one
This makes sense since they were probably originally held back a little bit in case they broke the game
If you're looking for high-synergy cards for the 99, then you'll have a blast browsing EDHREC dedicated Merfolk page
Rafael is very close to his cards and cannot tolerate their destruction, thus using a variety of Spell and Trap Cards to protect them, such as "Rescuer from the Grave" and "Self Tribute"
Others still, opt for an Abyss Soldier package, noting the synergy it has with Toon Mermaid (searched for with Table of Contents) and Salvage